Issues with Surefire 918FA (shotgun fore-end light)

OK, I have a bit of an odd question. I have a 918FA which is the 3-cell fore-end light.



The tube appears to be about 2x123a length, and about 1x123a fits in the fore-end itself to fit 3x123a when you put it all together.



I want to convert to using 2x17670 cells (I have appropriate light engine) so I figured I'd just add an A19.



Well with the A19, the two cells are too short by a fair amount (~1cm). Or, stated another way, the A19 is too long.



Is there a combination of components that will allow me to run 2x17670 with the 918FA fore-end?



Thanks,



-john