I think you can't. But remember that after hd install you have Debian testing/unstable and you can use APT to upgrade your Debian.

Code:
apt-get update
apt-get dist-upgrade
I don't know your configuration but usually there's problems with KDE after upgrading if old KDE is not removed beforehand. I myself installed Knoppix afresh from 3.4 CD and updated it then with APT. Now I have newist Debian with KDE and Gnome installed