Is it a balled or open cable? If open, just readjust at lock down point. If the cable really is two long, a bolt same thread pitch and size of adjuster bolt, but longer, drilled through to replace adjuster screw/bolt. Just remember to take a larger bit and drill a sink hole for the cable to slide in. You can also just buy bolts( really called a screw untill quite a large size, but enough of semantics) with holes in them already.
I've had this before, I picked up a cable kit from Walmart with end ferrels to make the housing the length you want. The kit had longer housings for rear brake and derailleur, I split one of the end ferrels and added it to fill the space. I've used several pieces on other projects since.