this is a newbie question i wish i would not have to ask... but here I am...
first a quick lay of the land:
vps (burstnet uk) running CentOS Linux 6.5, webmin, virtualmin
one domain name "domain.co.uk" and thank to virtualmin some web sub servers server1.domain.co.uk, server2.domain.co.uk etc.... all under bind9 supervision (configured automaticaly by virtualmin)
my first experiment would be to use bind on the vps to "redirect" serverXX.domain.co.uk to a fixed IP4 address w.x.y.z
after plenty of reading, i added one record (address) to the master zone domain.co.uk pointing to w.x.y.z
it now shows on the address list but any attempt to use serverXX.domain.co.uk from a web browser will end up being served by the "default" apache server running on the VPS.
Delete the sub server for serverXX.domain.co.uk and create a DNS record for serverXX under the virtual server for domain.co.uk -> Administration -> DNS Records. Since you don't need to create a website and email accounts for serverXX.domain.co.uk, you don't need to create a virtual server for it.