When adding to an existing ballon, we have the command to "Attach Ballon", which is good when you want to add ONE additional item to the ballon. It would be great if we could select multiple items, rather than one-at-a-time. Shift+select or a crossing window.... doesnt matter, just need a way to select more than one item. Seems like this would be an easy thing to add and would be a great feature.
Simple and effective

Thanks