I don't remember much of the movie so I don't know what the shot you're referencing looks like. When I was thinking about the Buffy project, I had thoughts about using the movie's introduction -- and Episode 1x03 (Witch) does feature Buffy waving pom-poms around at cheerleading tryouts that would match the ones of Kristy Swanson. I think I'll just stick to footage from the TV series, however.

The more the TV series revealed of Buffy's backstory in subsequent seasons, the more inconsistencies with the movie emerge, and the more evident it becomes that Josh Whedon does not consider the movie as part of the canon.

I'm not a fan of the movie, but I'd definitely be interested to see how your cut goes. Do keep us posted about your progress if you actually do this (as I will with mine . . . if and when I get started with it).