Are you talking about the lifting strakes?? If the weld is broken and the pontoon is cracked you are taking on water. If your pontoons are compartmented there isn't a way to the that water out. Pop rivets will only make a hole where there wasn't one, more water in. JB Weld is glue, won't hold any pressure. Get the part welded, won't take that much time and will fix it right the first time. Any 'mickey-mousing' you do now will only cause problems down the line