How do you create reseller nameserver when WHM won't let you assign IP?

Hi,
I'm trying to transfer one Reseller from another server to our server. All his accounts have been transferred and everythings done EXCEPT WHM won't let you setup the Resellers nameservers. I try to and it says that an IP is already assigned to them (which are the IPs on the other server) how can I transfer his nameserver to my server? Currently all his sites are down because he's already put our new IP's into his nameserver at his registrar. I gave him the IP's because they were the next available IP's and previously WHM always assigns the next available IP's to new reseller private nameservers.

Can I please ask cpanel.net to spend a few hours updating and improving their nameserver scripts, especially relating to resellers. The nameserver management is kind of patchy and unclear. I have much praise for the way the rest of cpanel works but if you guys are looking for areas to improve - please take a look at the way you've got nameserver management setup - its confusing and doesn't work sometimes, its pretty significant because it can cause sites to go down for fairly long periods if problems arise. Plus could you consider enabling resellers to transfer their own sites from server to server using only their reseller password.

Thanks.