The key to this design is that the cables are under a lot of tension from the spring plus you don't really need a dual hole sheath to keep them seperated. I think I can cut the sheath (already done) and add a length of bicycle cable sheath in the middle. Get both outer diameters roughly the same size and slip a 3" or so length of plastic tubing over the joints and then tape them into place. The sheaths will be pulled together anyway from the cable tension and the tubing will help keep everything lined up and prevent kinks at the joints.
Here is the cable I found.
It has 49 strands of stainless steel and is 0.030 diameter. 1/32" diameter is 0.03125" so that's about right. The nylon coating can be a problem, though. I ended up burning it off. Maybe a different brand of cable can be found without the coating. Either way, it should be no big deal.
This cable is refered to as 7x7 which means it hase 7 big strands and each one of those has 7 individual strands. That's where you get the 49 strands from and what makes it so strong and flexible.
I counted the stock cable strands and found about 49 so I'm sure that's what the factory used.
