To have the Lineup Optimizer generate lineups from a smaller pool of players, please follow the steps below:
Exclude All Players using the Actions menu.
Include the players you would like to add to the small pool of players by clicking the red X in the EXC. column. This will include the player when you optimize lineups.
Once you include the players you would like to add to your small pool of players, click Optimize Lineup in the sidebar to generate your optimal lineup, or you can go to the Multi-Lineup section to generate multiple lineups using only the players you have included.
Tip: You can view the players you have included in the Lineup Optimizer by clicking the Player Filter menu and selecting "Included Only".