OK there are a couple of ways to go about this. First is the somewhat iffy way, get your floor jack and hook one end of the spring around the axle and the other end off of the jack platform. Jack the spring up to extend it the amount you need. Then take pennies and put them between the coils. Be very careful installing the spring cause if the pennies slip it will pinch rather badly.

Second (preferred) method. Use the jack method as described earlier. Cut a piece of exhaust tubing in half lengthwise the length that you need for the spring. Weld a couple of washers in each end of the 1/2 pipe and install. When you extend the springs to the end of travel it will loosen the jig to remove it.

Lots of luck
Dennis