Pickling an {Exif,Iptc,Xmp}Tag itself

I'm on the way writing a small GUI for copying individual tags between files. That's when a problem arose: How to serialize a tag, e.g. pyexiv2.exif.ExifTag ?

The simplest way would be to stuff a pyexiv2.exif.ExifTag into a QTreeWidgetItem as QVariant data payload. But it doesn't seem to support pickling:
"RuntimeError: Pickling of "libexiv2python._ExifTag" instances is not enabled (http://www.boost.org/libs/python/doc/v2/pickle.html)"

proposed workaround:
=> "As you found out, your best option to serialize a tag is to pickle a tuple (key, value), which will allow to reconstruct the tag later. Pickling an {Exif,Iptc,Xmp}Tag itself is not directly possible at the moment, but it would be a nice enhancement."