Do NOT substitute anything for the elastic!
The elastic is important: it allows a snug fit both around your brow, while the bag is filling, and then around your neck, after you pull the bag down into place. In particular, it provides a flexible seal that simultaneously keeps an adequate pocket of inert gas in the bag and allows the excess inert gas to escape past the elastic, thus flushing away the CO2 that would otherwise trigger the hypercapnic alarm.
If you mean an alternative way to thread the elastic through the tube at the "hem" of the bag, you can do a couple different things:
1) Tape the end of the elastic to something like a pencil stub, that works like a needle, allowing you to work the "needle" through the tube, pulling the elastic along behind it. That's easier than trying to thread the elastic on its own.
2) Roll the edge of the bag into a tube, but don't tape it. Nip the slot in the tube for the elastic to protrude from. Unroll the tube, put the elastic in position, and roll the tube again, this time with the elastic in place, and tape it.
(Can you tell I've spent too much time sewing? It's astonishing how life skills can be applied to ctb preparations.)