Do they have a choice of any of the appetizers? I would say just use your existing appetizer group as your modifiers choices but I assume the big basket is also a part of that group and that could cause an issue.
You would just create a modifier group for your basket choices and set the modifier pricing to no additional charge, choose more than one modifier can be chosen with a minimum of 3 and max of 3, and add the appetizer options as modifiers.
