FYI I just tested and it is possible to get a group together in Hyperlobby Coop and then launch the game from hyperlobby, setup the server, then launch Banks GUI and then launch the mission.
Ill do some test missions tomorrow for whoever is around.
Here's the Banks Coop GUI Guide, you can find the download there too along with installation instructions. Basically the host just installs it into your missions folder under 1C softclub and launch it to select the mission. (Only the host needs to have it installed.)
http://code.google.com/p/il2coop/wiki/UserGuide