Would there be any way to use QC functionality in Windows within an FFGL wrapper
Well... Yes and no. No because Quartz Composer is largely dependent on proprietary Apple technologies like Core Image and the overall Quartz framework. But yes because those technologies are in turn dependent on the GPU, which can be addressed from any OS. When it comes right down to it, Quartz Composer is just a nifty graphical interface for easily stringing OpenGL commands together. If you have the patience and time to do the dirty work, there's no reason QC patches can't be ported to other formats. I don't know that much about FFGL but VVVV or just straight GLSL come to mind.
Personally I prefer anxiously holding my breath till the Resolume devs implement full on QC support! Quartz Composer FTW!
PS So what's the word on QC4.0 and Snow Leopard support then eh?