Alright kids, a bit of good news ...
The gaffers tape (mostly) worked, as you can see from the pic. There's some ever-so-slight concaving on a couple spots on the outsides, but it's really tough to discern in normal light. I think the flash from my camera is highlighting them a bit more. So yeah, it's not a 100% perfect dome, but it's darn close. At the very least, it's good enough to not be annoying.
For future reference to anyone who may have the same issue, I chose the gaffers tape because it was stickier than masking tape, and though it's not as sticky as duct, it comes off very easily and won't leave a residue on the surface. Having said all that, the real trick was to pull very quickly rather than a slow pull. I had read that somewhere and was a skeptical, but sure enough, it was the key to success!
Thanks again for the advice ... and happy to be part of the Salk family! I've spent a few hours listening to these, playing with positioning, etc etc. I can't make any real judgements yet, but I'm definitely enjoying these speakers and I expect to spend a lot more time with them in the coming weeks.