Silveroak is right here about encasing someone. Take a look at the box on p.30 of HoH:S, which is specifically there to address issues of Magic Resistance, and you'll see numerous cases where a magically created thing can surround and entrap someone.
We discuss here touching someone with a magically controlled flexible talisman long enough for a R: Touch spell to be cast, not encasing her.
While I agree that you have to touch at the right moment, e.g. the exact moment of casting, and that that may make the finesse even more challenging, I fail to see how RAW implies that you need to keep touching for the duration of the process. The quote you give only uses the present continuous in the example, and then only as a sufficient condition. There is no mention of continuous touching being a necessary condition.
At the end of the day though, my narrative sense says that it should be possible, and just awfully difficult. It won't happen often, and when somebody does muster the required finesse, it will be a cool effect. YSMV.
By its privileged position in the chapter Ranges, the text is describing the act of spellcasting with a Range in general, using R: Touch as an example. And it does so with present continuous. Were it not necessary, why use present continuous in that place?
By all means use your narrative sense in your saga!
If necessity was a conscious choice of the authors, why not state that explicitly?
It might just be that the authors did not think that deeply about the distinction, choosing the exact phrasing arbitrarily.
It might also be that they did think it through, and deliberately left it ambiguous to give our narrative senses more wiggle room.
ArM5 core has very little space for so many detailed rules. From the place of the text, we can see, that it describes the functioning of Range in general.
This is also very clear in the following, like in particular:
A spell that has a continuing effect remains in effect even if the caster moves out of range.
In the text's position, it is quite clear, that moving out of range while still casting the spell causes it to fail.
Expecting a reader to always dither, whether an author really means something, would have made ArM5 core half the size again - hence never been printed.
You were just talking about burying someone in clay, were you not?
Back to the OP, I finally found it. This may be the most relevant case for discussing a magus's touch through MR:
One of the weaknesses of invisibility is that an invisible weapon is kept out by Magic Resistance (and an invisible character’s touch is likewise kept out). (HoH:S p.32)
So, if the Talisman is under and effect that will be resisted, like the invisible magus, that should keep the character's touch out.
Now, if it's just the Talisman under no special effect, I personally consider it more like a magical being, which does not need to penetrate to mundanely contact the target.
I did look that up. And I also looked at your post immediately following it. That's why I was able to say silveroak was correct on this point. Come on! Please don't make false claims about what we've each done when it's especially clear you did discuss burying someone in clay:
We are not talking about detail, but clarity. ArM5 core has spent a lot of space on many words which obscure more than they clarify.
To sum up my take on this:
Stuff created temporarily by magic can not touch a being with MR, unless it penetrates this MR. This holds also for oodles of clay created around the being.
Stuff only moved by magic can touch a being with MR lightly without penetrating this MR, but on doing so its magic-induced motion ceases immediately without further affecting the being. This holds also for a magus' shoelace-talisman controlled by magic.
To deliver a R: Touch spell with such a magically controlled shoelace-talisman, the magus needs at least have it touch the target while he is casting the spell. This control interfers with a target's MR: hence the casting process of the R: Touch spell depends on overcoming it.
A strong Penetration of the shoelace-talisman's magical movement is hence critical.
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Of course, touching the target might not be limited to having the end of the Talisman just touching. Could also include the Talisman draped over the target's shoulders, or looped around an ankle
Yep.
ArM5 p.85 has:
Things moved by magic can cross the resistance, but their motion cannot, unless the spell penetrates the magic resistance.
A normal rock thrown by magic stops at her skin or clothes. The maga feels the warning that something has been resisted, and also feels the rock touching her (before it falls), but she is not struck by the rock.
So getting the shoelace-talisman into such positions without it magically moving across the MR would require a lot of clever play, lenient SG or Finesse.
I imagine the talisman magically crawling into the target's path, forming a snare there and having the target entrap itself in it - while the magus still holds the other end. 
The typical problem with such an undertaking is, that the target might still notice and avoid or brush off the talisman before the spell is cast.
The magus has indeed the same problem, if he touches an unwilling target with his hand for a R: Touch spell.