It might be because I explicitly keep the big blade of my offiziersmesser not Very Sharp but only Slightly Sharp, but all I need do is take the wire, emplace it upon my thumb, upon it emplace the knife, and then roll the wire around slightly (therefore making the blade run around the circumference), using only low-to-moderate force (the insulation is not a wundermaterial by any means (usually PVC, IIRC?)).
Thereafter it should be a matter of applying moderate-to-high force to pull it apart, or of repeating the process a two to three times a couple part-turns later.

That's how I do it but I've quite dexterious programmer fingers (and carpal tunnel, oh well), so it might be different in difficulty to pull off with full-size hand-work hands, but I hope this was quite helpful nonetheless.