How to redirect special query to internal server ?

[P.A.]

What I would like is to route all: w3.*.* querys to an internal HTTP
server used to develop clients web sites.

 OnLine ones would be for example: www.client_site.com  and local one
w3.client_site.com

 Actually we use the local host file, but we would like to avoid it
and configure only the DNS server, if possible.

 We use an internal Bind server, serving local and forwarding external
queries.

 Thanks in advance