I'm sure someone has done it, but it's not a good idea. Putting a .004" on one ring will cause stress on the scope tube at both rings. Plus, it reduces the ring diameter by .008", which is excessive. You should match ring and tube diameters to within about .005" to minimize stress on the scope tube.
Raise the base instead using beer can material (.007"), if necessary. Shim the front or rear of each base to get the rings parallel to each other. Then lap the rings.