Thats some work involved rigging for that one, but still not hard to do. Thing you will need to keep in mind is expected load of limb and what kind of shock load you might be expecting (being clothed lined by you're track line makes for fun times watching it, but not being that guy). Set you're track line might be a good time to consider a double track line for more strength when going to lift or just for weight reasons. After doing so you will have to set up a raise and lower line. This is going to be controled by two points. First point is going to be the guy lowering and raising and the other is going to to be with two prussik cords where the line drops to the load and comes back to the trollie. This is where you will run into some issues. you're climber is going to have to control the prussiks so the line can be lowered and raised.
This can be made as complex as you wish by having haul lines to move the trollie eather direction. This is used all the time by rescue teams to send a rescuer out over a victim lower him and raise the rescuer and victim back up and bring them back to a point. I have pics of this being done I think I might have video also but I am at work so I will check when I get home.
