I would also start him off with hyperextensions before doing squats or deadlifts to make sure his lower back is ready to handle a load.
Nothing major, just make sure that he can maybe do at least 2 full sets of 10 before starting him on any heavy squats or deadlifts (you are starting him light to learn the form anyway....right?)
I did that with one of my housemates who had a weak back and it worked out fine, no injuries.