Hi Ron,
I received a pre-release version of the Magic Pie Edge three years ago, and I asked GM if it would be possible to make up a parallel connecting “Y” lead to allow both the Bluetooth unit and the BAC-601 Smart Display to be used simultaneously.
The reply was,
"this involves two way communications, so it only supports one device at one time".
Without having more information
(and a much better understanding) regarding the protocol used for data transmission, it is difficult to say whether the two devices could be used simultaneously without one device affecting the operation of the other one.
If the BAC-601 could be made to work by simply reading the data from the controller that was being transmitted to the bluetooth dongle, it may work, but then the mode button for selecting the different pedelec levels would be unusable if the BAC-601 unit was unable to send data back to the controller.
I also mentioned that if it was not possible, perhaps a future option would be an LCD display with integrated Bluetooth connectivity, but as far as I am aware, there's still no sign of it becoming a reality.
Alan