Take a stapler and staple it inside-out (so the folded prongs are on the outside). Works like a charm, as long as they aren't stretched to the absolute max.
The way I did it with baby dry's size 6 was to reinforce it with paper tape (the yellow kind of tape) and just tape up where the stretchy stuff connects from the back to where the tab is in the front. It was more so that it could stay on in the night for me so it should work.