MainMenu with Custom MenuItems in design time

Question

Hi How do I add a custom MenuItem on a MainMenu,ContextMenu or Menuitem? Is there an event I can override? I have made a collection designer property on them all, where I can add custom MenuItems, but that only works when using the property editor. What I whant is, when u have f.ex. the MainMenu activated and click on an empty menuitem field, that a custom MenuItem is added instead of the standard MenuItem. Any hints, workarounds or articles? I can't seem to find any. TIA -spif2001