I'm doing the same this coming Monday 4th Nov. I'll report back.
I was chatting with KARFA last week and we concur that as long as the airbridge connects to the aircraft you can just walk up it and wait at the top by the glass doors through which boarding passengers will enter. Someone will see you and should let you through. I would still mention it to the CSM though so that they can alert ground staff. You must hope that the CSM is not in an unhelpful frame of mind. One previous poster wrote that the CSM told him that they would not alert ground staff. Nearly all will help you though.
The danger here though is that if the airbridge isn't connected you have to board the bus at the bottom of the steps and go the long way around - fast! This is rare but did happen on one of Karfa's flights recently although, fortunately, he wasn't on a B2B.
If you are forced onto the bus you need to be at the front behind the driver to be able to get off first - see helpful post 604 above regarding this.