I think you could make an insert between the TB and the IM out of thin Al plate or something like that with a vertical plate incorporated into it that would extend back to the cast divider. This would induce a split from right behind the TB.
If you rotate the TB I think it would cause the air to go to one side of the upper IM more than the other at part throttle as it would "direct" the air into the IM parallel to the butterfly as it opens, only at WOT would it provide even flow to both banks. Not good, as one side would get a lot more air than the other. This would cause some weird/dangerous engine problems, lean on one side rich on the other. Yuck!
The easiest, I think, would be to make a plate that conform the the back wall divider, you would have to notch the bottom to clear the PCV inlet and it would extend forwrds to the IM opening. Then you could wedge it in and/or JB weld it in place.
PS Terry when are you going to employ me? Sounds like THM needs some manpower!
