I don't know that that is actually possible, would be intereting to see if it can be done but insofar as I understand it the mortgage isn't transferred to any third party, the bank agrees to pay over the income from a set of mortgages to a third party. That third party can also then sell on all or part of that income to another party. Your mortgage payment may be going to a myriad of different parties in a slice and dice of income to different financiers.