Add cronolog package
pkg_add ftp://ftp.sunet.se/pub/OpenBSD/4.0/packages/amd64/cronolog-1.6.2.tgz
Configure Lighttpd to use cronolog
CRONOLOG = "|/usr/local/sbin/cronolog " + LOG_ROOT + "/%Y/%m/%d/access.log" accesslog.filename = CRONOLOG