I thought the thing to do here was to advise them to take out a credit card and rebuild their score that way, make purchases and pay off the amount every month without fail. Sounded pretty simple to me but they've checked back and no credit card company will accept them, even ostensibly those for people with bad credit 
If they've even been written off by those companies then what other channels are there? AFAIK their credit score is in the 300s on experian and they're repaying a credit card which eventually went to a debt collection agency.