You don't NEED extra weight. You never need extra weight. It is only a tool that we use to overload our muscles.
Especially if he is injured, he should be looking to increase his time under tension. If he's going for more weight with a back problem then he's just crazy.
I would suggest rack pulls.
By all means I would stay away from good mornings. Even at 100% these are very stressful on your body.
I personally would be doing movements where my back is in a safer position such as seated rows, lat pull downs etc. I would also be avoiding overhead work and anything which will subject the spine to vertical compression (such as standing with a weight in the hands).
So substitute for deadlifts, rack pulls. I personally would give the spine a complete rest from load for a few weeks.