Clear costmaps from within local planner

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I am implementing a local planner plugin for move_base. Under certain conditions I would like to clear the costmaps (both local and global) from within this planner. This turned out to be more complicated than expected:

• From within the planner I don't have access to the global costmap, so I cannot simply use the costmap API.
• Using the service /move_base/clear_costmaps does not work as it blocks the planner (probably because the service is called from the same node that provides it).

The best idea I had so far is writing a separate node that provides an action to call the service... But I am hoping that there is a less hacky way. Any ideas?