You can do as Goirish has stated. Or here is another little trick. Find yourself paper long enough for the entire length of the aileron, use newspaper or tape several sheets of regular paper together. Now lay the part you are preparing to cover over the paper and mark the location of each hinge slot on the paper. Now when you are done covering use that as a guide for relocating you slots. Once you have the area you can push on the covering with your fingernail to find the exact slot and then cut it with your hobby knife.

Ken