Good point - I hadn't spotted that in the datasheet.

It looks like all of the OSC pins can all be connected to ground - as long as you inject a signal into the SYNC pins.

That could be done from the parallel port, and could even part of the charge-pump circuit (if there's no signal, then don't clock the devices). Although I don't know how the L297 would cope in such a condition.

Although you could just use the ENABLE pin for that...