Well, you got the concept right, but doing it all at once using latex rubber creates a lot of problems. If you have to ask, you probably won't get it done. The thing is, latex rubber cures by drying. If the layers are too thick it doesn't dry well. Two seperate layers can be easily put together using the same latex. Doing it all at once only makes sence when your making only the one face, using the inside (wich will automatically be a negative of the same face) as the second face.
Trust me, I've done this a lot.
By the way, are you sure latex was used in MI?
Johan.