I want to hide my T-Mobile SyncUp Drive under the dash of my Escape. I'm thinking I can use one of those y cables from Amazon, and putting the second part of the Y where the original OBD2 port was, so scantools can still be connected (smog, diagnostics, etc) but anybody who steals the car won't notice the device, but I'm curious if that actually works. How can two devices be on the OBD2 bus at the same time?