Well, dispel magic is a curious question. If you've judged that won't work, no big deal. There's Mass Make Manifest from Spell Compendium, Transdimensional Spell from Complete Arcane (and Complete Divine, and Unapproachable East). Or if you want to be mean, use Dimension Lock. They're on another plane, and now they're trapped for the duration of the Dimension Lock (can't change planes). And the plane their in will cease to be before the Lock expires....