The ULF modules with the pairing button are a pain in the ass. You have to hold it down as you turn the key if I remember correctly. I have the ULF system in my '03 M5, but my X5 has the TCU module.
This video might help you. The system the guy is using is not installed in the car and he is using a switch as "ignition on".
https://www.youtube.com/watch?v=dJi0NUWQQQ0