We actually do this really often.

1. Either we fund in a separate account with a separate login.
2. We provide an offer for you to get permission from the reverse to fund in the main account.

We need there to be room for us to fund behind the reverse, usually a reverse does that but sometimes it doesn't clear up enough room.
We wont fund more than 40 days behind a reverse but we will refi 60% paid in and potentially buyout low balances.

Our goal is to come into a deal when its leveraged and clean it up and slowly, give bigger healthier deals for the merchant.