Can't you bypass then adding dns server on client? Also I don't think that's how it works, secondary dns, etc are not used unless the primary fails but I could be wrong on that.
Not sure if it is just crap filtering or not working at all. I'll add the dns servers to the router directly tomorrow and give it a whirl. OpenDNS works very well using DDNS a bit restrictive maybe but you can tailor it to your needs.