Assisting in sin - finding a subtenant for a flatmate who currently already has a subtenant

All my flatmates are muslim. one of them has found a subtenant, who is a Muslim friend of mine, who he will allow to stay in his room in August in exchange for paying his rent for that month. Subletting is prohibited by the contract. I also am away in August. I want to find a replacement for my friend (who is my flatmate's subtenant) by finding a replacement subtenant. I want to then let my friend stay in my room, which is called "lodging" and has been allowed by my landlord. My friend, will then stay in my room and pay on my behalf if he wants to or not. This will also relieve my Muslim friend who will not have to pay all of august. Is getting a replacement sub-tenant for my flatmate assisting in sin, even though he has one already?