another one just thought of that would require a major tweak, but nonetheless:

A leve where you can battle off with a massive baddie in a 24-manned group. could be set to activate as a special leve you get one a day of, max 5 stashed at a time, from the GC leve giver in the area. Level of difficulty of said baddie would be 40, going up to 55. Or whatever, just so it would be big enough to justify doing for the experience, Gil, etc. Another interesting, coordinated effort to level up your character.

Once everyone has the leve, you activate it, and they are all part of the party.