Forgive me for answering my own question, but after 2 successful attempts I've got it down. Not that knowing what to do helps that much...

1. Be VERY patient. Once it gets tough, you'll be pulling less than a mm at a time across the edge of the rim.
2. Be VERY strong. Your hands will hurt. It will take a long time. TIP: wear some full-finger gloves with little leather thumb protection tabs if you have them.
3. Go in ONE direction. With most tires, I work both sides at once, toward each other. With these, I'm having more luck starting at the valve stem and working all the way around clockwise.

YMMV. HTFU. All that.