The top and bottom cuts shoud not be too much of an issue(Don't do these until you have your face trim done).
It's the face trim that will be more difficult.
The best way I have found in this situation, is to do small stacks(say five).
Carefully lower your clamp using easy pressure over the spine edge of the book before you trim them.
This will flatten the books so you can get a more true face cut. You may have to play with the pressure a little to get it just right so you don't damage the book at all. Hopefully you don't have too many to do because it can be a little time consuming, but it does work!