Personally, I would wait till tire threads are low enough for replacements. Save one with decent wear for spare 20" rim (factory with same style as rest, just no sensor) and be done with.
Why is that you don't have a spare tire in your truck? I'm pretty sure you'll be able to find the one you want on eBay, shop around for price and free shipping. The spare won't have tire pressure sensor on the rim but it will get the job done.