I did not test it, but you can try this:
You can create a new website with ISPConfig, after that create the directories webmail and tmp into the /web folder of the webspace. (webX/web/webmail & webX/web/tmp). WebX is the webnumber as provided by ISPConfig.
Then copy the content of /home/admispconfig/ispconfig/web/webmail into the webX/web/webmail folder of that webspace.
Make sure that you've defined the right permissions.
You can enter your webmail at http://www.yourdomain.com/webmail/
If everything works, you can delete your previous Uebimiau as i've explained already.