Let me elaborate. The Body ECU is mostly needed for the immobilizer system to function. The other function is to get the signals from the Engine ECU to be displayed on the electronic dash.
For the immobilizer two solutions - kill it fully by modding the flash in the engine ECU, or build a small immo-fake module with an Arduino. If you know the electronic key code, that is doable (and no Flash modifications are needed). What is the protocol to make it work it I described somewhere on nefmoto.
For the dash - well, many solutions possible, but again building a small CAN unit out of Arduino that can translate CAN signals into analog ones that the Cinq/Sei dash can understand is one possibility.
And there is a third issue - the ABS ECU. This is where the t-jet engine ECU gets the vehicle speed signal from. This can be neutrialised in the engine ECU flash, but then there will be no speed information in the ECU, and that is actually quite valuable for some operations (for example, gear/speed dependent power limitation to protect the clutch). Some of the engine ECUs should have the possibility to take an analog signal directly from the gearbox (the Flash program has an option for this), but the circuitry is not there on all the ECUs (mine does not have it).
In any case, all three issues can be solved with a carefully crafted Arduino code, one board with a CAN interface. There are even Arduino devices with integrated CAN. You then hook up the dash to this device, get the speed signal from the gearbox or ABS sensor, and hook it up to the engine ECU CAN system.
That simple