Congrats on your new Calfee!!! We also just ordered a Di2 Tetra ourselves and asked for the D-Fly addon ($60 or so) for that very reason. The D-Fly easily wires in and attaches to your rear chainstay. FYI, it also transmits DI2 battery level via ANT+ which can be received by Garmin Edge 810 and 1000 models. From what I've read and youtubed, the setup just takes a few minutes. I'd think this is a huge plus for tandemers... somewhat similar to the extinct Shimano Flight-Decks.