[curt.clifton]

Bob,

If you aren't using flags for anything else, you could use flagging to add things to your ad hoc list.

For your tagging idea, the search field includes matches in the notes of actions/projects, so you could put your "tag" in the notes. A quick Applescript could be used to add/remove the tag text. Put that script in your toolbar and you've got a custom toggle switch. Custom meta-data would make this more robust.