You could create 5 Guest Star stories for each character, so everyone can have an appearance in the other characters lives. They might or might not all become aspects. You are going to end up with more aspects than usual, but that should work.
Another idea would be to create a sort of guest story chain. A's first adventure leads to character B's guest story with A appearing in it, which directly leads to character C's guest story with character A and B in it, which leads to character D's Story in which A, B and C appear, and so forth. I usually do something like this in game, so the characters meet one after another, but here you have the opportunity to make that happen before. Every one character could (or maybe even should) have a heroic appearance in those stories, them stepping in to save the other characters or something like that. A story like that is also bound to present some great hooks for further adventures.
The rest of the first stories and guest star slots can be filled as usual, only one character would have to "sacrifice" his first adventure slot, but seeing as it is the hook to bring the gang together, I don't think it is that much of a sacrifice.