Just finished doing my ball joint this morning. Same snag with the lack of lip, but mine had been butchered by someone and only about 2/3 of it is there, so I guess the boot will come off sooner not later....wish I'd read this post before I did everything back up.
I did manage to avoid the "fiddly swine of a job" with the top retainer ring, though. I looped 2 tie-wraps through the ring at 3 and 9 o'clock to the split in the ring. A simple job then to stretch it apart and slip it over the top of the boot. Felt quite pleased with myself for a minute or two.