[Exim] over-riding local_domains question

Hello,

I am VERY new to exim, but after poking around the config file and some docs, i think i found a solution to my problem. so lets back up to the problem.

i have a host/server that is home to many domains. basically a re-seller box. So frequently i created accounts for new domains before these domains' NS records actually point to my server. This causes me to be unable to send email to such a domain with my default exim configuration because of i believe these lines:

lookuphost:
driver = dnslookup
condition = "${perl{checkspam}}"
domains = ! +local_domains

now local_domains is set by :

domainlist local_domains = lsearch;/etc/localdomains

so i know I can either remove the domain from the localdomains file, but then i'd have to re-add it at somepoint, so what i'd really like to do is just always do the dns lookup when sending out email. if I comment out the line:

domains = ! +local_domains

Will that do what I'm looking for?

Thanks in advance