Changing the master for a slave domain

I figured I'd try using two domains and v6 to make it work with a dynamics master (sort of). I haven't tried anything yet, so I don't know if it'll work as I want it to, but here's my plan:

DomainA.com (the one I want to be a hidden master for, with HE being slave) and DomainB.com (HE being master directly).

1. Point my registrar towards ns2-5.he.net for both DomainA and DomainB.
2. Setup a v6-tunnel so that my hidden master gets a static and fully known v6-address.
3. Configure my hidden master so that it responds with AXFR to HE.
4. Create a new domain in dns.he.net, for DomainB.com
5. Create a new slave in dns.he.net for DomainA.com and point it to the v6-address as master.
6. Create a host (A-record) in DomainB.com as a DDNS entry with a password.

When I get a new IP on the v4-network where my hidden master is located, I can use the DDNS-entry from DomainB.com to set the v6-tunnel endpoint to my new v4-IP. Once that's done, my v6-network should work as before, which means the HE-slave for DomainA.com can reach my hidden master for the same domain again. No need to change the master (which doesn't seem possible), and still possible to automate in full.

I don't know if I'm making things more complicated than they have to be, but it's worth a shot.

Seems this was pointless. I can apparently change the v6-tunnel endpoint address without the need for a second domain, which means all I need to do is to configure the HE-slave to go via IPv6 to my hidden master to keep it static.