I don't mind writen an howto. In fact I document my steps for myself, so this would just need an cleanup if I'm done.
Currently I'm using drupal in single site mode. So the drupal code resides in an subfolder of an ISPConfig-client.
At this point I have some trouble to setup the rewrite rules. Well they are working but I had to manually add an rule to handle applications in subdirectories on the same level as drupal. I will do some test and maybe I'll report back in a sec and cry for help