I agree that raising the seat on the wheelchair would make it unstable. How about a scissor lift on a small scale? My dad had one made to lift motorcycles to a comfortable working height, about 2' or so max. It had a base about 2'x4', which stayed flat as it was raised. It was on casters. It also had mounting bars to fix the bike to, possibly these could be used to hold the wheelchair once it's on the platform. Collapsed, it was about 6" high, and had a short 'runway' to enable pushing the bike up onto it. There was a typical screw jack to do the work of raising it. It might be possible for the user to crank himself up to height, and down again, so he wouldn't be trapped 2' in the air if noone else was there. He could likely propel himself around using a broomstick or similar. I can imagine that something like this would be handy in the home, not only the shop, and the casters could be upgraded to work on carpet and lino without damaging either. If I were building it, I'd make sure it would get through doorways, and around corners, hallways into rooms, etc.
I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-