Cannondale puts grip tape on some of their pedals for some urban model bicycles and Ergon pedals use that strategy as well. I've had a close look at the pedals in question and think that a paper templet could be cut and then panels out of grip tape. The pedal area is flat and the contact area large enough that it should be effective - in fact - I might do it myself.

Not convinced that paint will adhere well enough, but epoxy sprinkled with sand might be a good alternative.