Kool Stop makes a tire-jack - one part fits on the rim on the side of the tire you do get on. Then you get as much of the second side on as possible by hand and have the other side of the tire-jack straddle the rim. It has a hook that grabs the bead on the part of the tire that won't budge. Pull back - and the tire is pulled up and over the rim, mounting the tire.

VAR makes a similar device. Both are lightweight and can be stowed in your bike-bag. Or your pocket. I was surprised as all get out at how well these work! They really do! No more BIG Park levers.