A group of Wizards would be pretty good, I think. Each of the Implement Masteries sort-of emphasizes a different role (Wand:Striker, Orb:Controller, Tome:Leader, Staff:ehhhh). Wizard abilities target non-AC defenses, and you'd have superb control over enemies. A lack of melee attacks is offset by superb range and close blast powers (ie, Thunderwave). Summoned creatures can act as HP sinks, and Wizards have a surprising number of defensive options (Levitate, Shield, Expedition Retreat).
The biggest weaknesses of the party would be health and skills. Luckily, these can be ameliorated with feats. You'd probably want one of your party taking Skill Training in Stealth and Perception to act as a scout. Everyone else should probably be taking Durable at the least. Another one should probably take Alchemy instead of Ritual Caster and make Potions of Healing, which are pretty decent for Wizards up through 7-8th level.
This is an interesting challenge, I might try it when I get home.