I have a friend who is a genius with a sewing machine, and she also has sleep apnea. I showed her my stretched out P10 and she suggested getting some real elastic from a fabric store to make a replacement headgear. I bought some elastic about 2cm wide (3/4") and cut a piece an appropriate length to go around behind my head and connect with the cushion holder. Then I take the piece and dip the ends into some oil-base paint or varnish about 3cm (1.5") and let it dry. Finally, I take a razor blade or similar sharp tool and cut slits in the ends where there is varnish - like making buttonholes. Now I can remove my bad headgear and hook my elastic into the cushion holder to replace it.
I made one of these about four months ago and it's still going strong. Oh, and I just use one strap, as I found the one that goes over the top of the head to be useless anyway. The genius part was to use varnish to stop the ends from unraveling and give them strength.