The Streamlight seem a bit big. The SF L1 would probably also work on "low" mode, but also suffers the size issue.
I recall Don had hacked a E1 with a Newbeam. I don't recall seeing how hard it was. Seems like it might be more acceptable size, but still not tiny.
The other thought I had was to get one of the Firefly and turn down the module very low. I'm not sure what that would do with the runtime - I assume it would probably be pretty good.
The bummer is all of these solutions seem pretty expensive, and in all but the Firefly are pretty large.
-john