I am pretty sure you have a misunderstanding here.
nslookupis used to analyze DNS information. The article you referred to is about synchronization of directory informations. There is no real link between these two topics.
So I am trying to understand what you really want:
You have a site which have no connection to the other sites, but has connection to the master site, correct?
When a DNS request comes in for “internal.domain” you get different replies based on DNS round-robin, right?
So if a client on the separated network requests information from the domain it might get as an answer the IP of one of the other sites and tries to connect. This will fail as there is no connection, correct?
So what you want is the client always getting the IP of the master (or the local backup/replication) to send its queries to.
If this is waht you want I guess you have to redesign your network. By design ActiveDirectory synchronizes information between all servers so they all have the same information. You can not overwrite this information on a single host. There might be a solution to work with sites or OUs, but I have never really tried it.
Sorry for not having a better answer for you.