Conditionally adding Context Menu Item in Outlook 2010

In my outlook 2010 AddIn, I want to add context menu Item when user right click on Appointment Item. However I don't want to add context menu item blindly, instead context menu Item will differ if user belong to different user group. How can I achieve this functionality with XML configuration file. I can add context menu item with native code but don't know how it can be done using config file.

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