1. In the board admin interface, on the Swimlane tab, convert the drop-down into a multi-select so that the board can support multiple swimlane groupings.
2. On the Active Sprints view of the board, add a drop-down above the board to allow the user to choose which swimlane grouping to use.

Extra credit: let the admin choose the default swimlane grouping so that users aren't initially confused.