Update.php with Multiple Administrators

I host multiple client websites on one code base. I need to allow clients to update modules and would prefer not to have then change update.php. Is there a way to allow users who are not admins to run update.php without altering the file?

Sorry if this is answered somewhere else, but I haven't managed to find even a hint of the answer after more than an hour of searches.

Thanks in advance.

Zanlus