Hiding Ribbon Buttons if a user does NOT have specific permissions on O365

Hi,

I'm trying to hide the "export to excel" / "open with explorer" buttons in the UI Ribbon for all users EXCEPT for those in a designated sharepoint group.

I can hide for all with the following :-

<CustomAction
      Id="RemoveRibbonButton"
      Location="CommandUI.Ribbon"><CommandUIExtension><CommandUIDefinitions><CommandUIDefinition Location="Ribbon.Library.Actions.OpenWithExplorer" /><CommandUIDefinition Location="Ribbon.Library.Actions.ExportToSpreadsheet" /></CommandUIDefinitions></CommandUIExtension></CustomAction>

.... but I only want to "run" the above if the users are NOT in my specified group.

I know I can include the "Rights=...... " definition within the custom action but I'm looking for an equivalent of "Rights<>".

In this respect, I'm only wanting it to be available to those who are site owners.

Is this possible declaratively?  I'm on O365 and would prefer not to have to tart about with masterpages if possible.

Thanks

Steve