There may be ways of doing this without MuVi. Chapter 6 of RoP:F gives some interesting RDT for use with faerie effects. Some of these could be suborned for the use of Hermetic Magic (remember, the RDT in ArM5 are not the only ones available).
Firstly there is Range: Prop
Since a Familiar and his magus are always considered at Range Touch, you might allow that the two are touching (I know that these are not strictly equivalent), and therefore the familiar acts as a prop. R: Prop might only work for inanimate objects as intermediaries; that would be an SG/Troupe call even if this effect is allowed in the first place.
Next there is Target: Medium
The requirement for an applicable Sympathy Trait is more of a problem here, since that isn't part of Hermetic magic. However, if you wanted to permit these effects you could hand-wave it away.
I generally bump a variant spell parameter up one magnitude from versions that are granted by a Virtue; and I consider these non-Hermetic parameters equivalent. Thus if I allowed this tactic, Prop would be equivalent to Voice Range (+2 mags) and Medium would be equivalent to Room Target (also +2 mags).
So, if you wanted to deliver your Pilum of Fire through your familiar, you need it to be R: Voice, T: Medium. As soon as someone comes within Voice Range then they are affected by the Pilum. However, you would need Duration on this effect if there wasn't someone already within Voice Range (I would rule that since the spell creates one fire, the Sun Duration would not allow the familiar to keep blasting people until the sun sets). Even without added Duration, the spell would still have a greater range - if your familiar is 15 paces from you, and your enemy is 15 paces from your familiar, all in a nice straight line, then your familiar could be used as a leapfrog to boost the spell a greater distance.
I would think Touch of the Familiar should be a ReVi spell rather than a MuVi spell, since you are not changing the spell, you are only changing how it gets there. Opening the Intangable Tunnel is a ReVi spell and this seems merely to be a special case.