Park domain(s) on another account upon termination.

I am currently doing this process by hand, and am looking for how I might be able to achieve the same thing Automagically.

Basically I need it so when an account is terminated (be it from WHM or API) the postkillact script parks all the domains on that account (unless the DNS zone was kept OR the domain(s) already have zones etc else where, and so long as the NS servers on the domains point to mine) onto another nominated cpanel account.

As for example at the moment I have a "Terminated" account which has a Terminated holding page explaining this account has been terminated blah blah this is the webhost... So while users domains are still pointing to my servers I can at least get some low level advertising out of them

How can I achieve this?

Also, how could I have a script which runs on cron and checks if domains are still pointing to my server(s) and if not, unpark them to save dns zone clutter?

Ps. If somecan write something nice for this willing to pay a modest amount, although if not pointers would be good for me to do it

Cheers,
Dan