I went out and bought some of that auto interior vinyl paint. The one I got was Plastikote Black. A word of warning: Although not stated on the label, this is a GLOSS finish.... I have since learned that PLastikote also makes "Flat Black", which I assume is flat, but the place I went to only had one "black"... Be sure to look for "flat".. I will have to hunt around for a source for the flat stuff.
Other than the gloss finish, it seemed to work pretty well.. MUCH better than regular spray paint. On my sample, the regular paint area I painted a few days ago is STILL rubbing off. The vinyl paint is nice and dry, and makes it look like the vinyl itself is actually black. Even retains the texture of the underlying vinyl material. Edge masking was not as crisp, though. The paint seems to have wicked under the masking tape a little, and looks a bit ragged. I will have to work on a solution, perhaps similar to the white-out idea, to resolve that..