Remembering and Adjustment Layer/collapse TF trick?

I vaguely remember one of the AE gurus coming up with a trick that stuck an Adjustment Layer (?) in between 3D layers in order to collapse all the layers below into 2D space... or something like that? It was something like pre-comping, but without the precomp.

Does that ring a bell with any one? My Googling skills are suffering this Monday.