What about modifying the trams so that the two sets of double doors can be opened independently of the front door?
Currently, there is a switch for 'all doors' and 'front doors'. What about making the switch a three way affair for 'front door', 'other doors' and 'all doors'?
If a B was in a stop that was to short for all doors, might this not be a solution? The result would be the tram having an overhang at both ends of the stop, thus 'protecting' the stop, with the middle doors open for boarding and disembarking.
Who knows, it might even start to encourage passengers to use the double doors over the single front door?