Reinstalling Explorer with Pacifist: Update problem

Neil Lee succeeded in using Pacifist to reinstall Internet Explorer (see yesterday's posting). But he could not then apply updates to this reinstalled copy (e.g., to update from 5.1.2 to 5.1.3). The update is only available via the Software Update System Preference and the Update application did not list Explorer. Apparently, it still believed that the updated version had already been installed. Deleting the Receipts file for Explorer did not help. Charles Srstka, the author of Pacifist, confirmed this issue.

So the question (similar to ones we have asked before) is: How is OS X determining what version of Explorer has been installed and how can it be fooled so that the Explorer update can get reinstalled?

Update: If you saved the Explorer Update Installer package file - when downloading it from Software Update (using methods described here before) - you should be able to reinstall the update with it.