Fenwick, no, I do see how what you're asking would be possible.
The bank would not want to add another borrower without qualifying that person's ability to pay. Rates being what they are, it could be to the (almost) husband's benefit to just refinance and add his (almost) wife on as a co-borrower.
As Rules stated, actual title to the property may be affected by their marriage depending on a number of contributing factors including the state they live in and whether or not a pre-nup is executed.
So the question becomes, does he want her to share in the property or share in the debt?