Okay so i want to point a domain to my multisite install.

Okay so i want to point a domain to my multisite install.
i have successfully done this with another domain that i own on the same hosting..

I'm trying to do this for a friends domain name and point it to my multisite. He's on the same host and has the same name-servers.

I have redirected using A name to my IP address. So now his website redirects to my public_html folder.. however... i have my multisite installed in an add-on domain folder.

How would i point his domain name to that? rather than my wp installation that is in the public html folder?