Please don't do this, it has massive consequences. I understand that it's only for your internal network; however, it will still break many things. Keep in mind that you're returning an IP for a live server, and as such many applications and services may think that something they're trying to access is really available when it's not. While this may seem trivial, consider a situation where an application is attempting to send data to a remote server and sees that it's up from behind your network; however, in reality the server has gone offline. The user begins to see unrelated (if any!) error messages about the program not working and calls you and / or your coworkers for support. Do you really want to troubleshoot that?
Here's ICANN's stance on it:
ICANN strongly discourages the use of DNS redirection, wildcards, synthesized responses and any other form of NXDOMAIN substitution in existing gTLDs, ccTLDs and any other level in the DNS tree for registry-class domain names.