Help... DNS Structuring Question!

[amir]

Hey all...
If I have delegated the sub-domains x.a.com and y.a.com to poeple , and
yet I want queries between
them not to have to go all the way to root , then to .com then to a.com
and then to the other domain,
but only go up to a.com , and he will refer them downwards ... this will
both relieve unneeded
load on the "." servers and make my queries faster... how do i do that ?
i've tried adding
the a.com as a hint in both the sub-domains files , didnt work..
what is the proper "rfc way" , to make one domain go straightly to
another ?
and please , dont answer me "forwarding"(lets say i want all the .com
queries to my ns begin at .com ,
cant send him a forwarding query , since it's recursive...)...
thanks for your time reading this ,
Amir .