http://iscoresports.com/

Is the only option to keep these is either add them up per game still or to just create one team called opponent and play all the games against this team? All I'm looking for is a line on the team website that shows the opponent's total stats that can filtered by league.

That is correct --- you can view any team's cumulative stats, but there is not a way to view stats from multiple teams as though they are a single team.