Painting cowl panel

This is one of those things..

you could get a can of spray paint (of your choice) and get the tube/cap setup off of a can of carb cleaner and paint down in there. (seen it done on an old dodge tradesman)

or by the time the car has 4 or 5 coats of paint on it, enough paint "should" have gotten down in there.

Otherwise no real way to get in there.