To be honest, I just made it all up as I went along.
I saw Mark's suggestion of being survivors of a crashed ship, so I figured the logical reason that we'd crashed is because the Founders sabotaged us. But then I had to think of a reason for the Founders to be so keen on taking us down, so I figured we may have stolen some Dominion plans. I then remembered the Breen raid on Earth, so I thought "maybe the raid was so weak because the Breen had expected Dominion reinforcments that were intercepted en route". So from there I just wrote up that we had intercepted the orders for the Dominion fleet to attack Earth.
It'll be very interesting to see what'll happen if the good guys don't win....the fate of the Federation is in your hands!
"You've all been selected for this mission because you each have a special skill. Professor Hawking, John Leslie, Phil Neville, the Wu-Tang Clan, Usher, the Sugar Puffs Monster and Daniel Day-Lewis! Welcome to Operation MindFuck!"