Another possibility -- a slide bench. Long enough to sit on outside the
tub, then scooch over to the washing position and then scooch back again.
With your setup it would probably need to be custom-built, but might be
easier than bringing the shower floor up temporarily. A hand shower with a
long hose (preferably longer than normal) is probably also going to be
Here's a stock version of a transfer bench, as a 'fer instance':
(Amazon.com product link shortened)
Your dad's physical therapy team should have some ideas of what might
work for temporary in your dad's unique circumstances.
Possibly useful free magazine for you and your family as your dad recovers:
Some stuff on bathroom mods:
Equipment like shower chairs and commodes and walkers can often be
borrowed from the local senior/adult center. Can be really nice to be
able to try out several designs without breaking the bank.