[TYPO3-english] typoscript: How to add a userFunc property to the config.baseURL property?

[Daniela Waranie]

Hi all,

i have RealURL running and a very long list of subdomains. The server is
configured to lead all subdomains (*) to the TYPO3 instance. For each
subdomain a typo3 domain record is defined in typo3 - introduced /
modified by an external programm. RealURL requires to set config.baseURL
to have all relative links (CSS, JS) working.

To have a long list of typoscript conditions like this is not good,
because i can not add the typoscript progammatically:
[globalString = ENV:HTTP_HOST=sub1.mydomain.com]
config.baseURL = http://sub1.mydomain.com/
[...]
[end]

The config.baseURL expects to get a string, but i want to have it more
flexible. I want to have the HTTP_HOST (input) to be checkt against the
typo3 domain records and is exists then use the subdomain as baseURL,
else use a default URL. (Input check is not my problem)

But how to extend the config.baseURL property have a userFunc result as
its value.
E.g.
config.baseURL = USER_INT
config.baseURL.userfunc = myclass->subdomainBaseUrlFunction

Sure this would lead into a core hack (or similar), but that is ok for me.

How to add userFunc support to the config.baseURL? What file to edit?
Code example available?

Please help
Daniela Waranie