Yes, I’ve done this numerous times! I typically will request a cash settlement for taking over their bad position but if they cannot pay all at once, I’ll take terms such as you are suggesting.
It might be important to have an end in sight for all parties so there are no ‘unknown’ factors. If the seller does not know how long his liability will be, he is likely not to agree…so make it X dollars/month for a certain time frame or X dollars up front with no further liability.
The key ingredient, I believe is that the seller will make this type of decision to relieve the unknown financial burden based upon his faith and confidence in you and your abilities to honor your contract.