DNS and port forwarding question

This is not a big problem, but I’m looking for a cleaner solution than what I have. I want to have a DNS mechanism for my WP server that works for the Internet at large, and also works inside my LAN.

I’m hosting my own server, and have a registered domain name. The DNS entry for my URL resolves to the static IP address I lease from my ISP. My DSL router port forwards port 80 traffic to the machine that hosts WP (at a static but non-routable IP address). No problems with that so far. Outside users quickly and reliably find my WP service.

But inside my router I need to use a different mechanism. Currently, I have a HOST file entry to redirect references to my WP machine to it’s local static address. That works, but is clunky.

For example, if I bring a laptop from my LAN to the outside world, or vice versa, then I need to futz with HOST file. Is there any way to configure things so that it works both inside and out? Could/should I host an internal DNS that only knows about my one internal address and sends other requests up to public DNS servers? Any other ideas?

Thanks!