In reply to:

But if there's a serial<->bluetooth adapter available, then maybe that could be used on the external port.



Brain Boxes has announced a Class 1 Bluetooth <> RS-232 adaptor. There's no mention of Linux support, however.
BlueUnplugged even claims they're currently available (for a mere $229).
_________________________
-Milton 100GB Mk2a / (DEAD)Tuner / Stalk Ford Ranger Republic of Texas