I did the same with one sk68, I simply glued on a 17mm driver without pushing it into the pill. And then soldered some copper wire on the side to contact the body for ground connection.
I guess if there’s room on this light, you can do the same. Otherwise some chopping off may be necessary, but the method should still work.
With the correct LVP settings (or LVP disabled) you can run them on 2x energizer lithium’s @ 3.6v especially when using an XM-L2 at low power (because of its awesomely low vF). I’ve done it on the bench with your BLF-SK68’s.
Guy looking for the driver currently (sorry I forget who and I can’t see cause I’m quoting WarHawk) I can send you a 1-mode SK68 stock driver if you want, if your in the US just PayPal me $2.50 for postage and it’ll go in the mail Monday.
You could shorten the pill the thickness of a driver then solder it on the bottom (if its brass), otherwise use some of that conductive glue or just mix copper dust into thermal adhesive.
Again this is comfychair’s picture, it wouldn’t let me hotlink it so I had to rehost…