So far we've had several solutions given including shifting the air in your BC to the opposite side, dropping weights and using a SMB or drysuit for buoyancy. There is at least one more not so obvious answer that no one has given yet.
well you could make your way to the anchor line and pull yourself up to the boat (Boat diving) and then use the trail line to pull your self along to the back of the boat if your shore diving just follow the countor of the bottom when feasible to where it gets shallow enough to stand up