don't do it. I did something like that last year with a section 8, single mom with a child, her boy friend, the dad of the child, aggreed to pay for the extra, I got the first three months extra before giving them the key, and that was the only I ever got from him, there was just no way to get a dime more from them. and they knew it was illeagal....they trashed the house two months after my first three-month-inspection. I kicked them out, but ending up to fix the house with more than 2000 dollars...
I will never ever deal with those section 8 any more, no more..