If the show is about Loud , the Only real feedback cure is a solid body electric mandolin.
Godin A8 would be a bit more acoustic sounding, but those are both Buying another mandolin .
try in-ear monitors, lower the stage volume.
pickups on acoustics hear the back of the room reflections and the monitors , and will amplify that too..
if the piezo strip is inlaid in the bottom of the upper bridge piece,
the top surface can be curved , it's just wood .
the thin strip of piezoelectric stuff doesn't take up much room.
Perhaps find someone knowledgeable to profile and re notch the bridge for best shape.
Look at the VOLUMES of prior posts on other peoples pickup discussions .
writing about music
is like dancing,