Roof MG question

Was there a way for them to be fired when the crew was buttoned down (all hatches closed). A lot of them are in weird spots where the commander couldn't just open his hatch and man it (such the .50 on Shermans mounted behind the hatches). Were they just for infantry fighting along side the tank to use? Also why not just use some kind of string and pulley system so they could be used button down, or is the coaxial good enough?