Well, I've never done exactly what your thinking either, so here's what I'd do:
- find an old kit part to practice on (if you don't have an extra piece of 'glass', let me know and I could send you one in the mail.)
- add some green food coloring to Future.
- dip the top of the windscreen in the Future and let it dry.
Assess the results and if it looks good, do it with the kit parts. You could try masking and spraying the area also, but dipping will give you just as good results without the prep/cleanup involved with spraying.
M.