I already thought of this idea myself, but i understand the issue that for example many duo games could potentially turn into solo games. Even though this thread is more than 3 weeks old at this time, i would still like to present my solutions for this issue:
The "no-fill-option" could be restricted to users with things like a certain amount of ranks, VIP-Levels, playing time, time since first joining CubeCraft. If that still wouldn't be enough, i would suggest CubeCraft to hire some volunteers who people wanting the option could apply to so they can see them play. Like that the option could be restricted to players who play very good.
I got this idea because I really enjoy playing duos for two reasons: fast generators and more difficult gameplay.
If I get put in a team with someone good, they often get many teams by themselves, shortening the game's duration. Also, since the purpose of two iron generators on each team's base is to meet the needs of two players, it would shorten the time spent farming. In my opinion, that's a great deal for having the option to account a w to yourself.
That would also make a good reason for a new leaderboard counting the wins of solo-duo, solo-teams and solo-mega-teams.
I would really appreciate it if this gets considered by CubeCraft Staff.