feedback source for 50 mask

[damstraversaz]

Hi
I'm actually testing a lot of possibilities with feedback source and have a some questions about it.
is it possible to use a feedback source as a mask for another layer ?

for exemple
layer 3 the clip with a dancer for exemple, like a traditionnal 50 mask mode
layer 2 the feedback source that could be a 50 mask too
layer 3 the masked clip
it could be grea to have just the feedback layer as a mask too
I try several things, but can't find a way to do this actually. trails is a fantastic fx, but does not give the same result.

thanks a lot for reading my poor english

Damien