Bundling - At least one has to be selected

At the moment you can bundle an item into another item and then mark it as mandatory. It would be very useful if you could say one of them has to be completed. Not that all of them are mandatory but that at least one has to be selected and completed in order to proceed. Instead of creating a separate drop down with the item names and saying only show the bundled item if in this drop down it is selected and then mark that form as mandatory.