That depends on how much material is missing. If the original ones just pulled out, I have heard of people gluing tooth picks in the holes around the outside edge, then installing the new strap buttons, but I have my doubts as to the long term viability.
I would suggest you find a craft or hardware store and pick up a piece of dowel rod slightly larger than the diameter of the hole. Drill out the stripped holes to the same size as the dowel (don't go any deeper than the current hole), then glue the dowels in place. Let the glue dry for 24 hours, then redrill the size hole needed for the new strap buttons.
