Edit:
Here we go:
Download:
http://code.google.com/p/il2coop/downloads/list
User's Guide:
http://code.google.com/p/il2coop/wiki/UserGuide
Simply unzip the archive somewhere below the user missions folder (e.g. "C:\Users\<your user name>\Documents\1C SoftClub\il-2 sturmovik cliffs of dover\missions\Multi\Co-Op"). Load the mission, start the battle and choose a army.
You are placed into a dummy aircraft. By default the dummys are some Blenheims and Heinkels without guns and fuel, just in case some idiots try to start a riot while waiting for the mission start

. If you like you can edit the IL2Coop.mis within the FMB to choose different aircraft types.
Now you can open the
mission order menu and select a mission. Use menu entry 8 or 9 to scroll the list.
After a mission was selected you can select an aircraft and position (pilot, gunner, ...). Again use menu entry 8 and 9 to scroll the list.
Now you can start the mission.
Client players only can select an aircraft and position.
Known issues:
- I'm not sure if it is working for clients already, there was no one around to test it

- Not all dummy aircrafts are destroyed when mission is started
- So far I didn't convert the group and aircraft names to more pretty text.
- The army selection doesn't influence the list of available aircrafts. This means you can choose RAF but can select a LW aircraft for the mission.
Source code of course in the archive but also available online here:
http://code.google.com/p/il2coop/sou...oop/IL2Coop.cs
Initial post before edit:
Ok I have an idea.
It is not possible to build a ingame COOP GUI ourself at the moment (really I know what I'm talking about). But it would be possible to create a web-base coop lobby that allows users to register for one of the aircrafts of the mission and that will force the user into that aircraft once the mission is loaded and the player is connected.
Here's how it goes:
1. The host has to upload the mission file to a web service (via browser). The web service parses the mission file and creates a coop lobby for this mission that shows all available aircraft.
2. Users can access this lobby via browser (the host has to distribute the url of the lobby) and register their steam-callsign to one of the aircrafts.
3. When everyone has registered the host gets a .cs script from the web service that contains all necessary scripting to force the user with the particular steam callsign into the registered aircraft.
4. The host has to place the .cs file into the folder with the mission file.
5. The host then opens the server and loads the mission.
6. The users connect and are forced into their aircraft by the script.
Option: The host loads a dummy map until all users connected, he then post-loads the actual mission. Again the script forces all connected users into their aircraft. This guarantees that the mission is in it's initial state.
I'm open for sugguestions.