One way is to go to Flanders Cables on-line and find the correct end fittings. It's easy to cut off one end of the inner with a suitable dremmel cut-off wheel. Remove the inner and cut the outer sheath to length. Cut the same amount off the inner cable (less the amount that you already shortened it by cutting off the end).
Test fit the cable to be sure that both inner and outer are now the appropriate length, then clean up the inner cable and solder on a new end fitting. It's easier with a solder pot than with a soldering iron, and don't forget to splay out the cable end like a bird's nest, to form a wedge inside the new nipple (end fitting).
If that sounds like too much work, order one from Motion pro or similar supplier.
My preference is DIY. YMMV.