The way I see it you can either cut off the sleeve and weld on one that fits your needs. Like Puffs said.
Or you can put on an universal twist grip. I've looked on ebay and options are plety. The aluminium ones cauth my eye, they are less then 10$ and have a many holes to accept different lenght cables.
But as you've mentioned, most bikes use a barrel type nipple.
This can be fixed simply, without buying cables.
You can:
1. solder the nippel type you require on your cable
I've done that with a brake cable once, it is very strong
There are many tutorials and youtube videos.
2. cut off the nipple and use one of the screw type nipples
You can get those as a kit or buy seperatly
3. buy a slide on nipple or just make one yourself
I done that as well. You just take a pin thats the required size, drill a cable sized hole thru the pin and then another nipple sized hole to about half way. And then you just cut a slit for inserting the cable.