Trying to setup a dynamic MX response

[Steve Robillard]

I am looking to setup Bind to respond to MX request with a dynamic
answer based on the query.  It is important for me to get back a
response which contains the initial queried domain + a predefined
domain.

The desired result on MX queries :

Query    : a.foo.com

Response : a.foo.com.bar.com

Query    : b.foo.com

Response : b.foo.com.bar.com

Query    : *.foo.com

Response : *.foo.com.bar.com


Would anyone have a suggestion on how I could go about doing something
like this?  I am sure it would be possible to modify the BIND src to
do what, but I am hoping there is a simpler way to do this that I am
simply unfamiliar.