Just enter the name@handle data and it will try to give you a sensibly balanced match. (If it's not 10 players, it might suggest 5v3 instead of 4v4... not sure whether that's a bug or a feature.)
The balancing is done in a super simple fashion:
1) Make sure that the number of sci players in the teams does not differ by more than 1.
2) Attempt to balance DPS and (weighted) HPS among the teams.
Obviously there is much room for modification, i.e. attempting to balance according to the leaderboard scores, or use kill counts, but let's see whether this simple thing already allows for decent balancing.