I don't know much about E83 X3, but in my E39 (1998 528i), I bought a "emulator" on ebay for some $15.
Installed it to fool the computer into thinking that the seat is occupied.
That was 9 years ago, around 2012, so far so good in the 1998 528i.
I bought the ebay seat emulator for $15 and posted the procedure in
thread #6:
https://www.bimmerfest.com/threads/d...sioner.602138/