Everything I can think of bar one option; killing him with a piece of equipment that drains health and dragging his corpse away manually before reviving him. Not tried it as I have no such equipment, I think I sold my Baneful Gauntlets long ago.
But I have tried an awful lot. Even overuncumbered him and drained his stamina so he fell over as soon as he left but damn, he does love those trees.
you don't have previous save?
and in walkthrough there was solution to prevent him from leaving by engaging dark elves so when you go down they will attack you preventing virgil from engaging his tree hump (that might have been written before unofficial patch)
what about scroll of exiting, teleportation, or killing him and then resurrecting him next to the trees?
or leave a character in place where he gets stuck so he has to run in different direction?
you said you tried everything so you probably tried those methods :P