Ok, I just found the solution. There is an Option / Env Variable, that can be set:
* You can manipulate several configure options of suexec
* through the following environment variables:
*
* SUEXEC_SAFEPATH: Default PATH for suexec (default: '/usr/local/bin:/usr/bin:/bin')
* SUEXEC_LOGFILE: Path to the suexec logfile (default: '/var/log/apache2/suexec_log')
* SUEXEC_CALLER: Name of the user Apache is running as (default: apache)
* SUEXEC_DOCROOT: Directory in which suexec will run scripts (default: '/var/www')
* SUEXEC_MINUID: Minimum UID, which is allowed to run scripts via suexec (default: 1000)
* SUEXEC_MINGID: Minimum GID, which is allowed to run scripts via suexec (default: 100)
* SUEXEC_USERDIR: User subdirectories (like /home/user/html) (default: public_html)
* SUEXEC_UMASK: Umask for the suexec process (default: 077)