You can add any number of players to the batting lineup. Either from your team's GameChanger site or on the Scorekeeper app, just keep adding players. Each additional player you add, after you have occupied all fielding positions, will be added as an EH.
Additional Fielders and Batters from the Web
1) Open the Roster & Lineup tab.
2) Click Lineup.
3) Click Adjust Lineup.
4) Drag players from the Bench (on the right) to the Lineup (on the left); Save your lineup.
Additional Fielders and Batters from the App (4th Outfielder)
1) Start or enter a game on your iPhone, iPod Touch, iPad or Android device.
2) Open the Game Menu.
3) Select the option labeled, Settings.
4) At the bottom select Rover or L/R Center under Short Fielder/Extra Outfielder.
This will create an extra player to appear as SF on the scoring screen. Rover will create a player right behind second base, while L/R Center will create another player in the outfield.