I have a similar setup (if I understood the question right) for my account. I have the DNS set at my registrar instead of x10hostings NS servers.
This is how to do it:
1. The IP of your server can be found in the stats section of your cpanel (left side, click the top bar to expand, it should be somewhere down)
2. Create a new A record pointing to that IP at Zoneedit.com
3. Go to your cpanel domain section -> Addon domains.
4. Add a new addon domain with the same domain as your A record.
This is neccary because x10hosting uses shared servers, once you have added it, the server will recognise that requests for your domain should be served from your account.
5. You are all set now. Just wait untill the A record gets to DNS servers around the world (usually about 1 hour, mostly not more then 24 hours).
Be aware though that the server IP may change at any time, and you would have to update the A record again. (Not that this happens alot, but the chance exists)