Since you say within subVIs, I am assuming that you have the subVIs open their front panels when called. Each subVI must have the RTM defined when the subVI is created. You can use the same RTM for each one (use the open function in the menu editor).
If necessary, you can dynamically add and remove menu items using the Application Control->Menu functions. I have some subVIs that add items to the main RTM when they are loaded and remove the items when they finish.
Rob
