2 sidewall/top sheet types in picture above. Not sure how the process would differ for either as I've had no problems with both types but maybe I'm missing your point. In any ski consruction, there will always be some material from the topsheet coming down to the metal edge and it's the angle it meets at that makes the difference between it being easy to deal with or slightly more work. In my experience, whatever it's made off, it's soft enough to scrape away without a specialist plane & getting rid of a small amount of it when I've needed to has never been a problem.
Take say the first picture with a 'full sidewall', you only need to get rid of a little bit at the bottom of the sidewall face and exactly how much that is will depend on the angle it's made at. On the second picture, i.e. your CAP construction, it's just resin you'll be dealing with at the lip interface. I'd guess that if you're getting to the point of cutting into wood etc, your edges would already be too thin to make the job worthwhile.
Edited 1 times. Last edit at 18.36hrs Sat 29 Oct 11 by moffatross.