How to modify the open_basedir setting for one domain.
To change the open_basedir value when using php in CLI mode (not suPhp), you can do so by going to:
Admin Level -> Custom httpd configuration -> domain.com
In the top text area, insert this one line:
which is the default value in the templates. Edit the paths in that line to meet your needs.
If you're running CustomBuild 2.0, you may also need to add the path:
to the above list. Adjust php55 (for php 5.5.x) to the php version you're using.