Is this it?

Unless thats what this does, I dont appear to be able to configure name servers for specific subdomains? On the "Name-servers" tab, I can configure name servers for the entire main domain name, but not independently for any subdomains.
Taking a peak at CloudFlare, they actually have a "NS" type. Im guessing that is what I actually want (not TXT, which I presume is for having there NS serve the value I enter as raw bytes)? It however, wont let me enter a IPv4 address here neither, complaining that my entered "Content for NS record is invalid".