Bjorn,
The way we do it we use the double ender to wind up the line. Clip one of the ends to the line, and use it as a handle to wind the line. As a team, the person on the bag manages the bag, the other manages stops and the ascent. This really only works well when the non-bag shooter stays in front of the person handling the bag. That way the team is able to keep easy track of each other.
One trick, if your back-kick isn't perfect, is to use your fists to maintain separation. I'm still, uh, back-kick challenged, and when I do ascents with people and need a bit of separation, I just put my fists out. The other team member will extend theirs, and we'll gently push off as needed.
You could let the bag hang, but then you do run the risk of getting blown off the line or separated from the bag . . .
If you are diving with a can light, having a loop on the cord and an extra double ender to clip off the light on your d-ring hanging down (out of the team's faces) is pretty handy. That way, you can keep your light on, and relatively accessible if needed to signal.