I'm looking for something that does for the USB serial port what roquBT4 does for the internal GPS; i.e. let you select which source you want an app to use.

I've got a bluetooth to OBDII adapter but all the app store apps require a dock connector that does all the handshaking. The bluetooth adapter just connects as a bluetooth serial port on a pc/mac, so there should be a way to connect it to the iPhone if the stack supported it AND there was a way to inject the output to the existing wired com port.