get a small square of plastic. If you have any extra scraps just use that.
Get a box of snaps from walmart that are like this:
[ATTACH=full]83034[/ATTACH]
in that little square of plastic, drill a hole so you can fit one of the eyelets through, then hammer one of the snap studs on that...and then use Plastiweld from walmart. Its in a blister pack in a tube that looks just like this:
[ATTACH=full]83035[/ATTACH]
mix a little bit of that and put it on the back of that plastic square, and then put that square on the inside of your knees.
Then take some elastic and put the socket on the elastic, and now you have a snapable strap for your knees.