Aside from using Li-Ion rechargeables, you've got two options:
One, you could take apart the E2DL head (either yourself, or send it to someone with the necessary skills/resources) and replace its circuitry such that it runs at a lower voltage than the original 6V for 2xCR123.
Or two, you could buy an E1B and swap the front-most portion of its head with that of the E2DL. The threads/dimensions/etc. should theoretically be the same, so this should yield an E1B head (80 lumen high, 5 lumen low, operating on 1xCR123) with crenelations, and an E2DL head (120 lumen high, 5 lumen low, operating on 2xCR123) with a smoother, non-crenelated head.
Note that both of these procedures would void the warranty on your light(s), and also that I can't recall ever seeing anyone actually perform these mods. Not to say they couldn't be done or yield satisfying results, just that you might be venturing into uncharted waters.