I was often in the situation where the bus was packed and i could only get off from the back door. I seemed to always be able to get the driver's attention somehow to let them know i had a bike. Whether it was hollering or making eye contact through their rear view mirror. Maybe i was lucky to have courteous drivers but they always seemed to be checking their back door when i was getting off. I used to also let the driver know when i got on where i was going to get off so they would hopefully remember to let me get my bike at that stop.