Hi Falko. Thanks for your input as well and I realize it currently isn't supported. I am merely looking for a way to make a maintainable adjustment, which I don't have to apply with every ISPConfig update. ISPConfig updates always make me a bit nervous because I host a couple of sites for others people. Adjustments to the standard ISPConfig code, especially ones that I have to apply with every update, obviously increases the risk of errors occurring.
Have a nice weekend.