But now there are two solutions, although neither of them will sync with AvantGo during a regular HotSync -- they disable HotSync while they're running.
This is a freeware program that theoretically lets you sync AvantGo by just pressing the button as if you were doing a normal HotSync. I found it to work only intermittently, and very slowly.
If you have $19.95 to spare, this commercial program works much better for me. It provides an Internet gateway for your Palm so that AvantGo can do a "modem" sync, and other Internet-enabled programs should also work.