You do know the saying "You'll attract more flies with honey...", right?
I suspect the reason the responses have been minimal is that no one has a good answer for you. There aren't many 1xAA boost converters available, and I don't know if any of them are as small as .55".
TnC has some light engines based on MJ drivers that can support a single AA, but if they ever offered the drivers alone for sale, it's been a while. And I don't recall MJ offering any for sale recently (if at all) either.
The current "RV7" driver that Axel refered to is avaiable
here, but it's a little bigger (17mm) than you're looking for. I don't keep up with DX/KD/etc components, so I can't tell you if there are other options available there. Try asking in the
Flashlight Electronics - Batteries Included sub-forum.