So in overal, you're trying to achieve the following:
The realtime model, which isn't actually rendered because it's invisible plus additionally non-transparent should cast out a stencil shadow right ??
I've did some tests with this already in the past and my results were that the stencil shadow were rendered uncorrectly/unaccurate but I'll run some more tests to give a final view.
Btw, you really are unorthadox plus contradictorical

Cheers

Frazzle