Alternate Sub-domains in a Multi-network

I'm new at this and am not sure if I'll be able accomplish this.
How can I Use one site - for example:
JoesShinyNewNetwork.com as a working hub site for my multi-network but jsnnet.com for sub-domain creation assuming I own both?
In other words I want to give customers a shorter sub-domain name without getting away from the branded site. Thanks