Elmer's Glue on Canvas, then paint the whole thing. I have totally done this, but with a hot glue gun. Elmer's Glue seems to be a better idea since hot glue leaves behind strings and is harder to work with.
25 Great repurpose projects with spray paint. Don't throw away those tins cans, spray paint them and use them as pots, vases, or pencil organizers! -- 29 Cool Spray Paint Ideas That Will Save You A Ton Of Money