If you already have an H-bridge setup (or whatever) to run a stepper motor, then the easiest way to turn it into a step/direction interface is with a shift register. You'll need a bi-directional parallel-out shift register. Instead of hooking the h-bridge control lines to the controller, you hook them to the outputs of the shift register. You'll have to configure it to do circular shifts. Then the clock and direction pins of the shift register are hooked to the controller.
Unless you are controlling multiple steppers, then it's hardly worth the effort. You'd be better off implementing functions in software that emulate the behavior you want.
$0.02