The services / daemons ISPConfig uses are not compiled by the installer, ISPConfig uses the apache, sendmail, mysql, PHP, bind. etc. that belong to your linux distribution.
The only things being compiled are a second apache that is used only to host the controlpanel on port 81 together with the PHP needed for the controlpanel scripts.
So its not nescessary to tweak the installer to use the packages that you have installed with apt