Assuming you want to return to the anchor above, would it help to focus on a body haul with a 2:1 system using the rope that trails from his belay device? For example, if he has an ATC then the integrated biner can act as pulley (ATC becomes passive). Could you set up a haul system where his trail line goes up through a biner/pulley fixed above you and then back down to you. Then use your legs and prusiks/ascenders to pull down on that line.

I know there's a lot of missing details in the above (e.g., backups, how to reset efficiently). Also, at least the upper biner I mention probably needs to be a pulley or the friction from the two biners will likely be a problem.

Bill
Rescue Amateur