Theoretically, yeah, switching the tailcap to something non-resistored would work. However, to my knowledge, the tailcap of the LX2 (and L1, A2, etc.) is a unique size, and no other UI designs were ever implemented in this size. So back to square one: if you wan't a different UI, you'll need a different tailcap, which means you'll need a different body (e.g., an E2E).
I don't think I've ever heard of SF selling either LX2 heads or E2E bodies by themselves, but it couldn't hurt to call. Otherwise, check the MarketPlace here - there's a pretty steady exchange of parts such as these (well, might be hard to find just the LX2 head).
All that said, is the LX2 UI really all that bad? If you're okay with momentary/twisty, you should never need to use the low mode if you don't want to: just press all the way on momentary, and twist all the way on constant. Nothing to say you have to stop at a half-press or half-twist.
Of course, if you're set on having a single mode clicky, then you'll want to go ahead with your lego. Easiest for that, I think, would be to buy the two separate lights, put them together yourself, and then sell the extras on the MarketPlace. For best resale value, I'd recommend getting an LX2 and L4, so that the extra light to re-sell would be a 2-stage L4.
