A majority of airports in Northern Europe that doesn't have jetways, and alot of airports around the world, has direct boarding from the terminal to the aircrafts - so no bus are used.
PMDG refuses to add the option of starting the boarding without a bus present. At least for me, this ruins the immersion of having a bus clipping into the terminal in front of the aircraft.
This small mod removes the model of the bus. You still need to call the bus in order to start the boarding, but at least you won't have the thing clipping into the terminal right in your line of sight.
Note: read the included readme carefully - this mod is NOT just a drag and drop into the community folder.