Okay, photo time. I used 2" elastic and 2" stick-on Velcro. The hardest part was sewing through the stick-on velcro because the glue kept gumming up the needle. Wiping beeswax on the needle frequently helped. The hook side of the Velcro is sewn on the end of the elastic, and the pile is on the knee shell and pad. Be sure to set up the left and right sides so the ends of the straps are away from the frame so they don't hang up on the bike. I got all the stuff at a fabric store.
2" Elastic:
The stitching inside:
And the stick-on Velcro. On the padding, it's also sewn like the elastic.
Hope this helps.
Kathy :^)