If there were some kind of "shared tags".... Are there any functions and/or workarounds dealing with this?
Yes Data elements are basically used for returning results which can be passed across rules. (For eg:- you can set up a data element to capture the page name and use this across rules).
I see that what you're trying to achieve wouldn't be possible thru data elements.
As I mentioned earlier, DTM doesn't currently have this feature. You can, however, suggest this as an idea over at http://ideas.omniture.com/. If possible, kindly include a use case as an example as this makes it easier to understand the requirement.