I love having sore thumbs, makes me feel macho

Another trick, if you haven't already tried this, is to hold the wheel with the section opposite the unseated part pressed into the crease of your hips as you work on that last bit. Doing so flattens that side of the tire and creates just a tiny little bit of space around the rest of the rim. Usually makes it a tad easier to ease that last bit over the edge.

Hard to describe that, I hope it makes sense.