Answer:
I cannot fathom why a lender would suggest such a thing! Customers A&B jointly own real estate. Customer A applies for a loan to be secured by that real estate, and is credit worthy.
You'll need to obtain both signatures on the mortgage/deed of trust in order to have a valid lien on your collateral. But you cannot have B liable on the note.
While I cannot cite chapter and verse indicating your request would be a violation, I can suggest that you might be treading where you ought not go.
First published on BankersOnline.com 2/17/03