Custom MX record + A record for a subdomain?

Please disregard: answer found.

I have a subdomain I’d like to transition over to dreamhost slowly, one service at a time. To do this, I need to start with a custom A record and a custom MX record, so that all the domain’s services start out at the old server.

Someone asked how to manage a custom MX for a subdomain two months ago, and the answer was:

This almost works for me – but the DH interface forces an uneditable A record for the subdomain. If I go up to the main domain, the A record appears, but if I try to remove or edit it, it grows back (so now I have two A records for it).

I want to use DH’s DNS but I’m not ready for that A record to point to DH’s servers. Can I do this?[hr]
Answered my own question: If I go back to the domain listing and choose “Deactivate Parked,” the parked domain goes away but the MX stays, and I can delete or change whatever DNS entries I need.

What was the solution you found? It might be useful to others who encounter this problem in the future.