Measure the distance you need to fill, making sure you get the average of all three bump stops. Go to Wal*Mart, get two rubber mallots. cut them to fill the void. Drill holes through your mallot pieces. Go to your local auto parts store, and get longer bolts (bring one of the original ones with you, to get right thread pattern). Now place your cut mallot pieces against the metal, using your factory stop, on top, (cause they have metal washers, already inside of them. Now put longer bolt through both pieces, and tighten them down good. When you get all three of them done, in this manner, put your spare tire back on the mount, which should be sitting firmly, against your new, extended, stops. Total cost, about 4 dollars.
No Painting involved, as the rubber mallots, are black, same as your original bump stops.