Hi,
I developed a little stupid Squirrelmail plugin, which includes the webuserprefs page in the Squirrel options page. Together with the already built-in SQ auth mode, this allows my users to stay in their interface while configuring their SA settings.
So far, no changes on the WebUserPrefs source code where needed. I only cleared header.php and footer.php, configured the output options and enabled the SQ auth module.
I would like to add internationalization and consideration of SQ color settings, but this would need some tweaking in the sources. I could imagine some 'Squirrel-included-mode' configuration flag, in order to distinguish old and changed code. I also think that the resulting SQ plugin should be uploaded to squirrelmail.org, since there is NO configuration plugin with file support like yours.
If anybody is interested, the whole package (SQ plugin + webuserprefs 0.6) is attached. Unpack it in your Squirrelmail plugin folder and follow the README file.
Squirrelmail plugin as wrapper for WebUserPrefs