The proper way to shorten a cable only needs logic. Hold the cable up to the lever to find out how much to remove and mark the length. Keep in mind that cables need some slack to work properly. Cut the casing being careful not to damage the cable, a dremel works well for this. Now measure the length of the cut casing and cut the same amount from the cable itself. Find a piece of round stock, the unthreaded part of a bolt will work, and drill a hole just big enough for the cable to pass through. The hole must be countersunk on one side. Slide the cable through and weld it with a mig, grind or file it smooth and you're done.
If you don't have a mig the local welding shop will usually do this. Just make sure you have a Timmies card with $10 on it.
Buying a round will get you everywhere when it comes to small jobs --- within reason.