Thanks, all. I was just brainstorming an opportunity of circumstance.
This week I bought a spare (5th) OEM alloy rim on eBay. Couldn't pass it up at $55.
Of my 4 present tires, one is about 20Kmiles newer than the other three, as it was replaced under road hazard coverage. When the time comes for new tires, I'm thinking of buying a new set of 4 while keeping that newer tire on its rim as a spare replacement for the doughnut spare. Otherwise I may just store it at home, tire and all, continuing to use the doughnut as my spare.
Thanks for the tip on how to adjust the floor height should I decide to do this.
David