With the short amount of time that the '08 STi's been out, and the fact that not too many people have purchased them (thus putting '08 take-off parts on the market for the rest of us), I don't think there's much knowledge about what will swap over and what won't.
I think you're probably going to be the 1st one on SECCS trying an '08 TMIC swap onto a <'08, and in fact may be one of the first in general to try it. I think you're just gonna have to try it and let everyone else know.