So I may be off a little here, never having made hot process... why do you want to do the foam with melt and pour? With hot process do you not do the f\o at the very end... so could you not take some out add TD to it, maybe add some water and whip it a little then put on top? This was not hot process, but maybe HP could be done almost the same way.

If you do want to use the M&P on top I always do it before it cools off... if a little melts into the CP\HP I still think that would look ok. I am not sure you would get the two to adhere otherwise. Alcohol sprayed between the layers has never worked for me with CP\M&P.