The LLC's and Land Trusts work well.
A lot of good answers here.
Believe it or not being honest with the bank often works very well.
One other option, I know a subject too investor. He has 28 properties and does this quite often. the homeowner gives constructive notice to the bank. Where the seller writes the lender a letter letting them know that they are in a position to no longer pay the mortgage and they are giving constructive notice that they are giving the property interest to another party and submit the letter with the check and send it certified mail and verify that it was received. Often the bank will acknowledge that even though the due on sale clause is in the note, they ignore it and allow the new owner to assume the loan anyway and often document this on paper to the new owner.
The lender wants the income and a performing note and they do not care who pays even though it says differently on the note.