Using just one sharp single edge blade, I'm using the same technique to trim the overlapping piece of Monokote - e.g. on a wingtip - a difficult area that some modelers avoid using different colors on and also with compound curves. There is a learning curve and it takes longer, the tighter the radius you're following because of the small contact area with the blade. A flexible plastic straight-edge comes in handy here to place a Sharpie line down to follow; a paper towel dampened with alcohol can be used to wipe the Sharpie line away after the trimming process is complete and edge sealed down. I have also used the edge of masking tape to follow in place of a Sharpie line. If I encounter a stubborn place where the material won't start shearing, I'll slide the blade back and forth while pulling on the excess to start the shearing process again. I go through about 5 single-edge blades per model.

Note that the covering must be stretched past the trim line and the excess material must not be stuck down anywhere beyond the trim perimeter when trimming the excess off.