compositing and generating mattes for video.

[super gnu]

i have a scene where i wish to drop some cg into a video.. ive done tracking a million times, so there is no issue there.. my problem is the mattes and comping. its shot from a (sometimes slow, sometimes fast) moving vehicle, and there are numerous trees, bushes and buildings that pass between the camera and the cg elements. there is no "perfect blue sky" to use as a matte.

are there any "tricks of the trade" to generate mattes for blurred, fiddly objects like this? some clever software that can generate (decent) mattes based on scene movement? some camera trickery i can do to allow auto matte generation ( ive not shot the footage yet) ive seen the amazing new lytro video camera that can separate objects based on depth (amongst many other amazing abilities) but my budget is more "gopro/slr/shoot it on my phone" than "100 million dollar production" so thats no help. the thought of hand-masking all this stuff is making me want to ditch the whole project.

[super gnu]

Nobody? i was sure there must be some decent smart matting /depth matte software on the market by now..? google search shows dozens of papers on the subject, some dating back a decade.. and image analysis on gpu is so powerful these days.. do people still just cut stuff out by hand?!

[super gnu]

hm i found YUV soft 2d-3d suite, afx and nuke plugins.. can apparently generate depth mattes for a sequence, from a couple of hand painted keyframes. but. alas, despite looking promising, they "only deal with corporate clients, and deals of $10,000 plus. small companies and freelancers are not considered." great business model.