Galbadia Garden if I remember has a very similar if not exact disc thingy that Balamb has. Why would a sorceress have put it there?
Squall and co. had to tell Balamb Garden about the missiles, had to go down into the basement, and only did so in the hope of finding something.
I don't think you change the missiles that head for Trabia anyway, if I remember correctly you don't even get to the missile base before they are fired.

Norg was sitting in a specifically designed pod in a forbidden level of Garden, I think he did a bit more than give them money.

Oh and thanks by the way TogiB