Problem configuring own domain

[addemsx1]

I have a website up at addems.x10.mx, but I'm trying to host it on my own domain.

I own the domain addems.co.za, and am trying to add it as a parked domain to my free x10hosting domain according to the instructions given at https://x10hosting.com/wiki/How_to_Use_Your_Own_Domain.

I have sent a request to my domain registrar to set the nameservers, but the request was rejected with the following response:

The SOA record for addems.co.za at 99.198.122.2 can not be retreived.
!
! The most common reasons for this is that the Nameserver is not currently
! reachable or the Nameserver has not been configured for this domain.
!

The SOA record for addems.co.za at 108.178.57.230 can not be retreived.
!
! The most common reasons for this is that the Nameserver is not currently
! reachable or the Nameserver has not been configured for this domain.
!
ERROR: No valid nameservers found - rejecting request.

Through communication with support for my registrar, I have been told that they cannot point the domain to x10hosting's nameservers until x10hosting nameservers have been configured for my domain. Apparently this problem is unique to co.za domains.

I assume that the nameservers will be configuered when I add the parked domain, but of course, I cannot add the parked domain, and attempting to do so gives the following error:

Using nameservers with the following IPs: <IPs of my own nameservers> Sorry, the domain is already pointed to an IP address that does not appear to use DNS servers associated with this server. Please transfer the domain to this servers nameservers or have your administrator add one of its nameservers to /etc/ips.remotedns and make the proper A entries on that remote nameserver.

Because transfering the domain to x10hosting's nameservers seems to be impossible for now (I'm in contact with the registrar's support, but they don't seem to want to help), the second part intrigues me. How would I go about adding one of the current nameservers to /etc/ips.remotedns, and what are the proper A entries?

Is it possible to park a subdomain (e.g. www.addems.co.za instead of just addems.co.za)? I have tried setting NS records for the subdomain and tried parking it, but this did not seem to work.

If not, is there anyway to get this working with my nameservers hosted elsewhere?