You can still use the dope method, but you have to apply clear dope ontop of the maskings before you add the color, this way the color doesn't bleed under and onto the previously painted surface. Go light on application of paint, and after you apply your last coat, peel the masking before the paint dries, it's still soft and you can remove it before the paint "set's-up", so you won't have to worry about peeling the whole thing away.