Well, you could just create units on the map with no model etc. and make the spell require the unit. If the player researches w/e upgrade or w/e you need, create that unit in a secluded spot. Done, he can now learn it!
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.