You might be able to temporarily widen the lower half of the doorway by unlatching the right side of the door (outside looking in) and swinging the door inside as you do when folding up the TM. It would take literally just a few seconds to do, and you'd have to do it every time you wanted the additional clearance. You'd only get you 0.75", maybe 1", and only for the bottom half of the door. I'm pretty sure that is possible, but my TM is folded up and I don't have a picture handy of that area, so maybe someone can confirm.
What about using a narrow wheelchair, like the ones used on commercial aircraft? Aisles in the coach cabin of commercial aircraft are definitely narrower than the TM doorway. I believe they are ~20 inches, and those wheelchairs glide down the aisle with no problem.
Something like this:
Certainly easier than modifying the doorframe.
Dave