How to re-install ispconfig3?

I upgraded Debian 6 with ISPConfig 3.0.5.4p9 to Debian Wheezy. The Debian upgrade rewrote configuration files, but I did not find a way to run the ISPConfig 3.0.5.4p9 installer again. It refuses to run and says ISPConfig is already installed.
I got around this by installing the latest ISPConfig, namely version 3.1.1p1. This created the configuration files again, and all seems to work (except webmail with roundcube, but noticed it just now and did not troubleshoot yet).
I would have preferred to keep the older ISPConfig, since this is a multiserver setup and I was not planning to upgrade the master just yet.
Is there a way to get ISPConfig to rerun the installation or configuration step to get the configuration files? I was also going to remove mydns and install bind9, but that would also require running the ISPConfig installer to get the name service configured to use bind.

 

But doing
php -q install.php
just shows
ISPConfig 3 installation found. Please use update.php instead if install.php to update the installation.
end exits back to shell prompt.