What you'll need:
Sony PSP TV Adaptor (can probably find a cheaper version of the same type of thing somewhere else) (these things are as low as $5 buy-it-now on e-bay)
VCR (optional)
TV
Tuner card
Using the PSP TV ADAPTOR and a VCR, record all your stunting on a VHS tape.
Once your done with the stunting, connect the VCR to your computer using the tuner card and transfer your favorite/all the stunts on the video. Now isn't that simple...
other method
PSP into the tuner card, but this requires you to waste hd space on all the stunts you fail, and all the time spent not stunting (also comp lag might screw you over)
*you'll only end up paying about $10, and this is way better than using the cheat device*
*both these methods will work when gta VCS comes out*