Bartamos, I think your playing card trick would work better than that Eastwood gizmo. Getting paint on the outer part of the rim nearest the tire would be really impossible. Vertical blind slats with a curve in them would probably work better than the Eastwood thingy. One thing I've used is a hand-held masking device, but not on wheels. I just move it along as I paint. It would have to be custom cut to match the radius of the wheel.
