With some of my older, less expensive circulars, I preheated the oven to about 175.
Pulled out a large cookie sheet and placed the needles on the sheet.
Once preheated I turned the oven off and put the tray on a rack in the center of the oven.
I watched the cable and when they started to sag a little I pulled the tray out of the oven. Picking up the needles by the center of the cable, I ran the cables through my hands to smooth out the cables. Do Not pull on the cable needle join. Once all the cables had been smoothed I hung then needles in circular needle hanger.
At 175 the oven is about the temperature of many hot water heaters. In the oven the entire cable is heated at the same time, rather than small section under running water.
So far no problems with the join.