Your solution is pretty simple, especially if you are working in a larger scale. Whenever I sprayed the anti glare panel on my Mustangs I used Scotch Tape, the dull acetate or "invisible" tape. This will give you a very straight line, just make sure you press the edge down really well, then go over that tape with painter tape as you tape off the rest of the fuselage.You should get a clean line. If you are using "rattle can" flat black you got to make sure you spray from at least a foot away from the kit, sounds like you are spraying too close and that is the problem, so light coats of paint with short duration squirts. If you are using an airbrush, do the same thing, maybe use less air pressure. As for your windscreen just buy masks. The alternative is to place the same dull acetate tape over the various sections, then follow the outline of the framework with a new #11 exacto blade (scalpels just don't work well for modeling, use them for dental surgery where they belong) then gently press down against the frame edges. If you do it right using your steady dental hand you will have nice painted framework. Remember to spray from a distance with short duration spraying so the paint doesn't build up and bleed through. If you do get a little bleed through then after you pull off the tape you can clean off the edge of the framework with the tip of a tooth pick (I know how much you dentists love those things) and you should have a nice looking canopy frame work. Make sure you tape off the inside of the windscreen too. Hope this helps, but it is worth the few extra dollars to buy paint masks for the canopies and wind screens, although Mustangs and T-Bolts have about the easiest canopies to tape off.