but with some volume, I bet it would be a negligible difference.
Unfortunately, I don't think that there is any way that the cost of an entirely separate PCB plus 28 pins for the connector is ever going to be "negligible." There are companies that do this sort of thing in order to provide "backward compatible" parts for chips that have gone "out of production" in their original form, and they manage to charge quite substantial amounts.
(There is also the problem that the chip in question here is quite narrow, and actually implementing such a PCB would be substantially difficult.)