Works a treat, cutting this pesky thin inner layer of PTFE and not the wire
filaments.

Two 2inch lengths of 12mm diameter hotmelt sticks. Temp controlled solder
iron , melt a slot axially in one. With a pair of razor blades gripped in an
engineer's cramp with gap one end , wider than the outer PTFE, and the other
with blade edges touching at a point. Push the wide gap end into the
hotmelt. Cool and repeat with the other end. Mark along the razor edge where
the stripped wire falls to.
Push some of the sleeved wire down to just beyond this point and drop
hotmelt , filling the space down to the closed gap end.
One sliding cut and 180 degree rotation is all that is needed , slide away,
remove from the slot and pull off the cut sleeving.