Is there a way to auto-increment tag info?

Hi,

Trying to edit some tags for my This American Life collection so that iTunes recognizes as podcasts (to take advantage of the 2X playback and bookmarking).

One of the extended tags needed for this is PODCASTID, which has to be unique. Is there a way to auto-increment this extended tag so that file #1 is "0001 at http://www.thisamericanlife.org" while files #432 is "0432 at http://www.thisamericanlife.org"?

Thanks.

Create an action of the type format tag field for the desired tag field
Enter as format string:
$num(%_counter%,4) at http://www.thisamericanlife.org

Select all the files that should get renumbered. In your example this should be at least all the 432).
Apply the action.
The action always begins at "1".