...I was just going to solder the old nipple onto it.
In case you have not heard of it before (I realise plenty will have). A tip you might find useful is to obtain, or make, a very slim tapered bit of rod. A bit of suitable thickness welding rod or a large panel pin will do as a starter . Once you have passed the inner cable 'rope' through the nipple you are going to use, cut it off oversize (+5mm) Then open the cable strands carefully and evenly by pushing the taper down the centre of them, hold the inner cable at the other side of the nipple and tap the taper in as tight as possible. Then solder the whole lot together. Once cool cut off the excess cable and rod. This way the joint is not relying solely on the strength and quality of the solder. If it is done properly with a clean cable etc it will never pull through the nipple hole, as the more the tension is applied the tighter the taper becomes. In any case I would use a new nipple to avoid having worn areas that might compromise the fit, or dirt in the hole that will foul and potentially weaken new soldered joint.
I make all my own cables, I make the nipples on the lathe, just get satisfaction outa doing it I guess, anyway a tip published many years ago was similar to BTB's but the suggestion was to insert a small glazing sprag into the belled end of the inner in the nipple then solder, I have to admit I havn't done this for a long time but just rely on the same method as BTB, probably because I can't find my glazing sprags. kind regards