You shouldn't point the IP to the machine's main IP. There's no webserver listening on this IP.
You don't have to transfer the registration - just point the domain's nameservers to us. This is an /entirely/ different thing.
If you can't, or won't, do this for some reason, the best solution is to add a unique IP; this is less likely to change without notice. Otherwise, you can do a query on our nameservers to find the right IP to point your site to. This IP WILL change without notice at some point, and your site will break.