There's dirty disarm and a feat like follow-up strike (w/out the latter you're spellstriking the weapon rather than the wielder I think). Or dirty grapple.
You can already do it with trip, too, even without that feat.
The way DT is written, some DTs will use a weapon, but that's your GM's call. Some abilities like Cailean's Blade and Tankard always use a weapon for a DT.