Someone might know the answer; Otherwise I plan to look sometime tomorrow. I want to change the tuner frequency from within a program. Someone who'd done Linux stuff before might guess that drivers/char/radio-empeg.c implements a driver for /dev/radio and that the VIDIOCSFREQ ioctl would be what one wants. However, it's not compiled into Hijack, which means that's not what the player is doing.

Did I:
1) guess wrong on device name
2) miss some other interface for doing this that I should be using
3) incorrectly assume the player isn't monkeying on the i2c bus itself and just try compiling the module in

If no one knows, well, perhaps over the weekend I'll have some time and visit the car with a serial cable and try it.