Bark River usually does an occassional run of custom handled Fallknivens when current supply runs low, and they can squeeze it into their already hectic production schedule.
You would have to talk to Mike to find out if he would do an individual rehandle, but I know Bark River has outsourced most of their re-handle work, with the exception of warranty stuff.
You may find a re-handle on Fallknivens stock blade blanks designed for the kraton/rthermorun handles to be a bit small, but if you want to give it a try, you might have better success contacting some of the talented makers/craftsmen here on bladeforums.
Kevin