nothing exactly comes to mind but there is something you can try;
In a stand-alone host with one human player;
- bind a key to add a random bot (see fritzbot menu)
- and configure your host to force team balance as well as limit the number of players for each team. After you join then hit the key you bound to add the remaining bot. (you can also add the random bot in a bots file).
In a dedicated server the person running the server would have to do it in the console I think.
In theory there is a 'spawnbot' command that can be placed in a map script file, but I didn't get it working in some quick tests. Has anybody else tried this script command?