Geesh, it's not that hard.
Just put the MCU you in on your own (easy DIY, no?) and then ask them to "goodwill" the programming when you drop it off for the new Drive Unit.
If you run the numbers I'd bet you're still WAY ahead of how you would have come out with a Town Car, even with the days out of service, no?
Added benefit: every mile driven helps leave a usable planet for future generations . . . .
There is another thread where they tried the DIY MCU swap. TESLA SvC would not reprogram a customer provided and installed MCU.