I sold my 3P, because I never used it in original state - dim and the expensive batteries - but the idea to change the Light assembly is a good one.
for start try this here:
http://www.dealextreme.com/p/unique...en-led-flashlight-black-2-16340-1-18650-33550
open and get the light assembly out - put it into the 3P.
Of course the building of these cheap lights is not perfect, but doing the same, I got a Led Assembly that is really awesone; also put it into another host.
I am not completely sure if it will run with a normal CR123, but You might use a rechargeable CR123a ... that makes constant use of the light cheaper.
On the long run I would consider switching to a 1*18650 Li-Ion cell light (like the one You get ...)
the size is not that much increased, but it houses over 4 times the energy...
runtime: very very rough calc - that depends on the individual light assembly:
CR123a 800 mAh cell with single-die L/A: 40 mins
18650 Li-Ion: 2 hours +