I'm pretty sure there were two helm positions. The one in the conning tower was used when running an attack, but there was also one at the front of the control room.
A mod has been done to move the observation periscope to its proper position, but no-one has yet made the attack 'scope housing in the control room.
Photos are from U-boote Westvarts (1941) which (I think) was filmed inside an actual boat.