There isn't a mechanism like that in lighttpd. You can only check if a file doesn't exist. That means whatever rules you have after:
RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.*$ - [NC,L]
Will need to go into a block like this:
url.rewrite-if-not-file = (
)
edit: added equals sign
Because if the mod_rewrite rules that you have in your question doesn't get executed (which stops rewriting if the request is for a file/directory that exists), that means the request is for a file/directory that doesn't exist.