Hi Tomi,
Great question. Yes, you can do what you want with run-time shortcut menus in LabVIEW 8.0. If you want to dynamically modify the menu content, you have to do it in the "Shortcut Menu Activation?" event in the facade VI of the XControl. In the event data for this event is a parameter called "MenuRef" which works with the same menu primitives that have been around since LabVIEW 5 for editing the menu bar at run-time.
With these primitives, you can add/delete/modify menu items to the shortcut menu. The items that are already in the MenuRef when this event case executes are always the ones that are statically defined, either by LabVIEW or by customizing them. You do not have control over the state of the items that LabVIEW adds, but you can remove them and add ones with the same text (just with a different tag). In your case, you would probably want to use the Insert Menu Item primitive to add an item such as "Toggle State". Give it a tag such as "USER_TOGGLE_STATE". Then you'll want to use the Set Menu Item Info primitive to set the checkmark for that item based on the state of the XControl.
Then, you'll need to add an event case for the "Shortcut Menu Selection (User)" event so you can handle the item being selected. Wire the Item Tag parameter from the event data to a case structure and add a case to look for "USER_TOGGLE_STATE". And in that case, toggle the state of your XControl. That's all you need to do!
The Dual Mode Thermomter shipping example in <LabVIEW 8.0>\examples\general\xcontrols\Dual Mode Thermometer\Simple Dual Mode Thermometer XControl.lvproj is a simple example of how you can modify the menu and respond to the items selected. It's a little different than what you want to do, but it might help you to look at it.
Good luck! Let me know if you have questions.
Robbie