I can’t test it now, but doesn’t something like this work?
/ip dns static
add name=lan type=FWD match-subdomain=yes forward-to=<main router>
add name=something.more.specific.lan type=A address=<address>
add name=another.more.specific.lan type=FWD forward-to=<another resolver>
My guess/expectation is that it should. As for dstnat for router’s output, it’s possible too: http://forum.mikrotik.com/t/dstnat-in-output-chain/104694/16