Have you looked into the http://www.creationkit.com/EquipItem_-_Actor function? Not sure if it'll work, but it's worth a shot. Unless you're trying to avoid scripting, in which case, no idea how to do it! I'd check in the CK for anything, but it's being a tool and keeps crashing on load...
Edit: got CK to load, combat styles? There's a flag in there that enables dual-wielding.