The strap idea is a good one, but how can that be easier to install than an X-chock?
X-chock: place between tires, run wrench until firm. Done. Two steps, one sentence long.
Strap: Push one end through spoke in wheel, then reach behind wheel, pull through enough strap to reach through spoke of other wheel, reach from behind and grab end of strap, pull through to meet the ratchet, tighten ratchet. Done. Six steps, one short paragraph.
The nylon strap is slowly being destroyed by sunlight. The X-chocks are made of steel, no UV damage possible.
So, for more reasons than I already have two of them, I'm sticking with the X-chocks. You're idea is a good one, I just don't believe it is the better one. It's good thinking for how to solve a problem with what you have, though, and I give you a virtual pat-on-the-back for that.