Is there a good way to add a small piece of custom data to an individual
item (for example an integer used as a bookmark in the associated podcast
episode). The only thing I can think of is adding a custom "Tag" to the
item, but that presents several issues related to modifying and cleaning
unused tags. I was hoping that there could be something else (for example a
comment/note/special tag) that can be attached to an item
and retrieved back when loading the feeds items. There was at one time
support for sharing and sharing with comment but those seem to have been
deprecated after Google+ integration.

If adding a Tag is the only option, what is the most efficient way to clean
"empty" tags (tags that have no items in them).

Stefan