OK Cato, I have not seen anyone else post this method. Disclaimer: I have only done this once or twice, and that was a LONG time ago. The details are a little foggy. You may find better instructions on some of the military modeling sites as that is where I read it. As I remember, you heat one end of the sprue until it actually runs. (I think I actually caught mine on fire. I'm not talking forest fire here, more like an incense stick or match stick fire. If it does catch on fire blow it out).
Anywhoooo, you basically stick the melted end to your workbench and pull. I was able to get hair fine strands every time. Once the sprue cools it pops right off the bench.
I hope I explained this well enough. If you can handle a match stick flame, you can handle the sprue flame. I personally had more control with this method than I have with the holding the sprue over a flame method.