Oopsie, somehow I missed your last post:)
When I first rescued my Arab, he was really weak on the back end from an injury and we taught him to lean against anything. The wooden support posts for the fence, the barn, his stall wall, the farrier's trailer - anything.
Unless your horse has some sort of disease that he can't have NSAIDs, there is no reason why he could be on chondroitin/MSM and/or hyalurin/boswelia.
Both come in powder forms; just have to make sure you buy pharmaceutical grade that doesn't have fillers in them, so they will work like they're supposed to.
Edited to add: You aren't shoeing him are you? My ex-Trimmer was over six feet tall and did not have a bit of problem getting down on one knee and propping either of my arthritic horses' hooves up on his other knee. I only laid him off because I am no longer working, so had to take the trimming of four horses back.