I have been only few times really overpowered where I needed to bodydrag a bad situation. Yeah it's going to be exhausting so dont ride too tired when overpowered. I try to keep my kite low and just hold my front hand hard to upwind so I don't slide on the water downwind. Not so low that you have to eat water all the time but a bit lower than normal just to keep edging easier.
EDIT: moving fast is the upwind killer. You gotta try to get the speed down by edging hard with hand and feet.
Trim your kite to find the right 'spot' where it will hunt the edge of the window, but not too much..otherwise it will surge back and forward if too underpowered. Keep it low, with little upswings, then back down, ride on the front lines (depower rope), keeping enough power for slow consistent speed. Turn your head the upwind and the body will follow and position itself correctly. Push bar out all the way when bringing kite up and over 12 (to go the other way) and lean right back...do this too fast and you can lose the ground you already made up.
When super overpowered and want to body drag upwind, you can almost have kite resting on the water,and bar sheeted out. Arm that is in the water must also be at the correct angle. If the arm is too far upwind ie pointing into the wind, you will slip downwind. A kite that is too high when super over powered will pull you down wind very easily when body dragging.