You ladies done yet?

As for the OP, think about this. I've seen some old(er) school road headsets that used needle bearings top and bottom and had ultra low stack heights. They were threaded though, but depending on the design you might get away with just ditching the threaded locknut (further reducing stack height), and replacing it with a single thin 1 1/8" spacer or perhaps nothing at all.

It might not be the most durable or practical thing in the world, but then again, neither is the lefty