Map Main Site Domain Name

G'day Guys,

I have installed the plugin on a multisite and when activated it works fine. My domain has a dedicated IP and is accessible via that IP as well.

But I want to map a sup domain to my main site so the original domain name will not be visible.
This is what I have done now:

http://www.mainsite.com (multisite install with domain mapping installed)
created a record on sup domain: sup.otherdomain.com with dedicated IP from mainsite.com.
Added sup.otherdomain.com in the Domain Mapping Options (at http://www.mainsite.com)

Will this able me to show the main site as: sup.otherdomain.com?