Some time ago, I needed to have several subdomains working, without having to define them in lighttpd. The domains had to be mapped like this:
bredsaal.domain.com -> /var/www/domain.com/bredsaal/
testhomepage.domain.com -> /var/www/domain.com/testhomepage/
and so on.
Setting this up in lighttpd is actually VERY easy.
First, you should enable mod_evhost in /etc/lighttpd/lighttpd.conf by removing the # in front of it, in [...]

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