As far as I can tell there's no way to override a specific default context menu item - I would have preferred to remove the original context item too. The best workaround I can think of is to have a hotkey bound that doesn't conflict with existing menu items to avoid the cycling.

Edit: version 1.1 changes hotkey from I to M which should not conflict any other standard menu items
Edit2: using userChrome.css can achieve hiding the default #context-viewimage menu item