You stated he only uses cash or goes without and you both haven't used credit cards for years. Which begs the question: Why does he "need" to rebuild his credit score?
A credit score is a reflection on living with debt, year in and year out. Rebuilding a credit score is for the purpose of accessing debt-loans and credit cards.
Vehicle insurance companies sometimes charge a higher rate on premiums if one has a low credit score but it isn't a huge differrence. Certain very high security careers require a high credit score, again this is not the norm.
So, again, why does he "need" to rebuild credit if not to borrow money or access credit cards? Even if he suceeds in boosting his score the negative report of the bankruptcy is on his record for years and years--that is more of a hinderance than the score.