Hmmm. I just had another idea at Home Depot.
Can I use a compression-nut fitting (like the ones used to join the overflow and tailpipe to the drain's Tee-fitting) to connect the P-trap to the drainpipe projecting from the slab in lieu of the mission coupling? Or is that [a bad idea | likely to be a code violation] ?
What I have in mind is to firmly attach the adapter to the drainpipe, then glue the trap together and glue it to the adapter. The general idea being that if I ever need to redo it someday, I can cut off the trap, then nondestructively unscrew the nut holding it on to the drainpipe.
Assuming it's not bad or illegal, would it likely be a better or worse solution than the mission coupling?