Hello,
You really don't have to do anything special to do this.. If each of your servers have at least 2 static IP's that are used for it's nameservers, you can just tell your resellers to set up their nameservers with your IP's..
Say for instant you have a server,
ns1.domain.com = 127.0.0.1
ns2.domain.com = 127.0.0.2
Your reseller only needs the IP's..
ns1.theirdomain.com = 127.0.0.1
ns2.theirdomain.com = 127.0.0.2
Resellers don't have to have static IP's.. Most hosts charge for this yet anyone can do this on their own.. Its simply called nameserver sharing. For resellers that are doing this, you can optionally add their anonymous nameservers and SOA record details of them into the dns records of your server as well so it will maintain matches in the whois output..
I think all resellers should do this as allot of people use services like
http://www.whois.sc to find out where hosts are located, which datacenters they use and so on.
Regards,
Chris