But doesn't that mean you don't have am mouse wheel either? How the heavens are you browsing the internet and this forum without a mouse wheel? ;P
Either way, you can try your luck in
SteamApps\common\Divinity - Original Sin\Data\PlayerProfiles
and look whether changing the xml in EOC works or not. DEFAULT specifies keys, but only EOC somehow assigns them to game-actions.
Look for middlemousebutton and try to replace with a key that's not in use?
No idea if it works
