I recall user ZetaTre/lpcapital attempted to retrofit duramax NoX sensors and it didn't go anywhere. Search this and bimmerfest.
I still think your best route is getting a used NoX sensor for under 100$.
Also, despite mine being deleted, I'd recommend you prolong keeping your emissions components until the cost is close to $2,000. That's about what will cost to delete and tune. There are some drawbacks of going deleted.

P.S. Join "North American BMW Diesel Owners" group on Facebook. Plenty of expert advise there, too, especially related to tuning. Folks sell their removed emissions stuff there for pennies on dollar.