Like the subject says, I made a scenario that has all the races in the galaxy in a state of permanent war. This will prevent AI -- and the player -- from trading technology with anyone else. I also disabled minor races to prevent them becoming technology brokers for the major races. It's not a perfect solution to the problem, but it's a good workaround for now.

You can download it here. After downloading it, extract the file, and place it in GalCiv2/Data/English/Scenarios/ -- "Permanent War" should now be a selectable scenario from within the game.

My version has all races enabled, and the player playing as humans. To change this you have to edit the scenario file. They're just text, so notepad or emacs or whatever will work. To change the races that are in the galaxy, find the line that says "[ACTIVE]". There will be a list of all the races after that, one on each line, followed by a number. Change that number to 0 to disable them (or to 1 to enable them if you want the Dreadlords). To change the player race, find the "[Human]" line, and change the number after Humans to -1 and the number after the race you want to play to 0.

I'll also make an accelerated start version, but that'll wait until I finish my first game of Permanent War and see where I'd like the tech to start.