Leg-extensions, used as first exercise in order to pre-exhaust the quads work pretty good:
Two nice pre-exhaust routines
3 * 12 leg-extension
3 * 12 squat
3 * 12 hack squat
3 * 12 leg press
A squatless routine:
5 * 10 leg extension
5 * 10 hack squat
5 * 20 leg press
alternate with
5 * 10 leg extension
5 * 10 leg press
5 * 20 hack squat
It may take some time before you develop the condition to be able to leg-press / hack-squat really heavy weights after 5 sets of leg extensions, but once you can do this watch those quads balloon!