Since the client's account is sharing an IP with other sites, you have to use the ~account method to access the website, until the domain propagates.
Use the following syntax: http://ip.address.here/~account/ where account is the account's username.
Eg if IP address in your welcome mail is 70.87.12.210 and your user name is sample then you can see your site through
http://70.87.12.210/~sample