None of my bikes need a tire change for a while (I think/hope), but next time, I'll come back to this thread as a reminder.
What I usually do is stand the tire up on the ground, lube it, and jam one edge of the wheel rim into the hole as hard as I can. It hits the bottom of the tire/bead, and stays there.
I couldn't do that... sidewalls were too stiff. I had the edges lubed, and the tire flat on the ground. I put the rim on top of the tire and tried to push it into the tire... that's worked for me before. Not this time- not even close.
The rimlock didn't make things easier, either. Heh, my friend asked if the tire was the right size for the rim.