If you are looking for another option and comfortable writing custom actions, you could write an action to manage groups and call the action via webservice API.
With 2.1 actions do return additional parameter "result" in the NamedValue[] below which you can make use of.
ActionExecutionResult[] results = actionService.executeActions(predicate, new Action[]{action}); NamedValue[] values=results[0].getActions()[0].getParameters();
You could find more on custom actions at the below link.