This is a grey area where it will vary by saga. The spell binding mystery, for example, would not work, because it would maintain the presence of the summoned spirit, a spirit of form or spirit of spell casts its spell only once per summoning - keeping it arround longer merely gives you more time to instruct it on what to do. There's also the nature of such spirit which are in a very grey area which also makes it a saga-dependent issue over how these theurgical spirits are handled as regards the rest of hermetic magic. We have guidelines on how to summon and control Airy Spirits, for example, But RoP:M is explicit that it's not clear at all to anyone whether spirits of spells and spirits of forms can be classified as airy spirits.
What probably allows something along those lines are the guidelines in TMRE p. 28 for summoning and controlling a disembodied spirit - which spirits of spells and forms are. At the minimum, however, this is incredibly inefficient, if your gamemaster allows it at all. It would require, to give you an idea:
- Researching the hermetic theurgy spirit of spell or spirit of form, so that you know it exists;
- Finding an arcane connection that's not the actual theurgic spell to those spirits, if you want to summon it from afar. While most airy spirits will have arcane connections that can be found because they're a spirit of something (anger, an element, a plant...), this is not self evident for spell spirits and spirits of form since it's a disembodied spirit and it may not have existed at all before you invented the spell (see the debates hinted on re: airy spirits on RoP:M 108 and TMRE 78 for spell spirits). The normal alternative to an arcane connection is provided by theurgy which uses the name of the spirit, which can't be imbeded here. So for this to be possible in an item, your storyteller has to rule that a spell using the generic spiritual guidelines can incorporate the name of the spirit as an arcane connection, which is less than clear;
- If you have that arcane connections, 1 season to open an item, and 2 additional seasons on item enchantment to be able to summon and control that spirit from the item is a minimum.
If your storyteller rules the name of the spirit can't be imbeded, then you're limited to controlling / summoning those spirits at less than arcane connection range, which may mean the fake magus will need to be physically accompanied by up to 50 spirits of form to be able to replicate the normal versatility of hermetic magic, plus a few spirits of form/spells to encompass effects that require requisites. This would require 50 lab seasons at a minimum, most plausibly at least 1.5x that. Anyone with Second Sight will see the legion of spirits with him and wonder why a magi would want to be accompanied by so many spirits, and will make those spirits vulnerable to other magi's control due to their constant presence arround the fake magi (for lack of an option to summon it from afar). Unfortunately, even having those 50 spirits arround, the fake magi would still be unable to have them perform certamen on his behalf.
Even if your storyteller doesn't give you trouble for carrying a legion of spirits with you, the game system is less than clear whether they need to be summoned again to regain might, which may be why hermetic theurgy can't compel a spirit to do two spells without letting it be dismissed in the first place. Remember those spirits may or may not exist on their own outside of your magic...