Im sort of new to the game but could you set it up like this:
Duplicate ( limited to only one of, say 50 cp? to be normal ish) game starts with a duplicate, duplicate is different/less powerful ( up to you, to simulate being to different people)
Multiform this is your "gestalt form",trigger on (recombining with your duplicate), trigger off ( a time limit perhaps? because you cant maintain the form for too long or something)
then, switching back to your regular form triggers the duplicate
This is a basic idea of what i thought of, sorry i don't have the math all figured out.