Standard MoveIt interface for 2-state grippers

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In numerous manipulators, grippers have 2 states: open/close. Although it is interesting to get actual joint data from the gripper to get additionnal information, most of the time OPEN/CLOSE suffices.

Working on the integration of a new robot, I am looking for the most standard way to integrate the Open/Close commands in MoveIt that would also be handy to use:

• From an Open/Close button in the GUI (in the MotionPlanning display for RViz?)
• From code (A custom service with a custom srv? Some Python overlay to the MoveIt commander to command the gripper as a group?

What do you think?