Layer1 invisible when Layer2 facing away from the camera in an other comp

Hi

I've got a main comp with many Picture comps.A cam is flying from one picture comp to the next and so on.Each picture comp is made out of several

pre-comps.one of this pre-comps contains the frame of the picture.(3d layer)

my goal is now this=>if the picture comp(3dlayer) is facing away from the cam in the main comp i'd like that the frame in the precomp changes it opacity from 100 to 0 .

it's similar to Dan's expression http://www.motionscript.com/design-guide/invisible-facing-away.htm but with pre-comps.

any ideas?

cheers