improved option,
just run a jet lighter flame near the cord,
roll the cord around so a line around its circumference gets a light sealing.
using the side of the flame, not blasting with the pointy end.
jet lighters can have a fair bit of accuracy. and a heap of heat. they don't seem to use additional fuel. the blue flame seems to melt cord with less than burn and blackening.
actually, come to think of it, i held these ends right through the furnace while running the lighter past it, back and forth really fast!, so in the pic you can see where i've put the flame on it too long, it's singed -.-
p.s added photo shows zone of lightly melted outer