Continuing on MobsterOO7's work, I've made a fix for the opencoop mod by looking at the hex values before the float 9 (in order to filter out the relevant value).
for anyone interested:
http://www.megaupload.com/?d=J261A79G (feel free to re-host, i'm not in the habit of hosting files on the web, so I just took the first best service I could find that wouldn't cost me anything :D)
I've tested it with 2 players, one pc with three screens horizontally and seemed fine. There is one catch however, all the players in the server (and the server) need to be working with the same dll's and .pk4 files (apparantly). Which means, the people you are playing with need to have the same fix installed, which is probably not what you want if they don't have the same setup (3 screens wide) . The fix works as the ones described before, by changing the actual aspect ratio of the '16:9' aspect ratio. Which means if the people you want to co-op with have a 16:9 aspect ratio but not a triple screen, they are somewhat screwed (as they need to install the same fix). It might have been better to alter the aspect ratio of 4:3, as it not used as much anymore, but I havent got around to look for it.
Screenie for proof: