Lower Back Injury, Squat Alternative?

Having injured my back during summer 2010 (breakdown of posture squatting using heavy weight with minimal rest) I visited a chiropractor and was told that I have trapped a nerve in my lower back and since have been on a course of adjustments to rectify this.
With things feeling better after a 2 month break from lifting, I began on the I,Bodybuilder program where things were going well, until last week when I began the leg phase.

A long story short, I am looking for a substitute to the back squat for this program as having read many articles and forums I am torn between persevering with lighter squats or trying out hack squats.
I have never done hack squats so have no idea of their benefits/potential, and light squats just wont get the gains I’m after…
Anyone with advice/experience on the most affective alternative would be much appreciated.

NB I,bodybuilder back squat session is 6 x 3rep ramping sets

This probably isn’t the advice you want to hear, but I am giving you my opinion based on my experiences:

I’ve dealt with low back injuries affecting nerves, and in my experience, the most important thing to do is to rehabilitate your injury and correct your mechanics before returning to intense training. Your injury may have affected your mechanics at one or many joints, and if that is the case, returning to training without addressing the issue could likely result in getting injured again. I would advise against doing a program like “I,Bodybuilder” because it’s not individualized to your strengths, weaknesses, and needs.

As far as exercises go, anything with reduced or eliminated compressive spinal loading is the way to go. Sled pulls, glute ham raises, reverse hyperextensions (if you’re fortunate enough to have access to one), single-leg squats, Bulgarian split squats, and a large number of other single-leg exercises would probably be beneficial.