I need to change just the rear part of one of the brake cables. The part which attaches to the brake shoes and exits the back plate and then joins with the rest of the hand brake cable.

The problem is where it joins with the rest of the brake cable via a metal sleeve. Both cable nipples are firmly stuck inside the sleeve due to dirt/rust. I need to release one of the nipples from the sleeve in order to attach the replacement rear handbrake cable. I have done this before; but it took me hours: it's a real pain. It was years ago when I did it and I think I used a pair of mole grips to hold the sleeve whilst trying to prise open the part of the sleeve which gripped the cable nipple as I could not get the nipple to move to the open space in the centre of the sleeve where it would have simply come out off.

Does anyone know a better technique for removing the nipple from the sleeve?

THANKS