NAT-routed wordpress redirects to standard port

I have a website that I host on my main server (a Mac). I’ve got a Ubuntu server (lucid) running wordpress on a different machine on my site. My main server is NAT-routed port 80 -> port 80, as one would expect. I’ve got my wordpress server NAT-routed port 8888 -> port 80, the idea being I can point my browser from outside the firewall at https://www.example.com:8888/wordpress/ and reach my wordpress install.

This does not happen. What happens is that the wordpress at port 8888 then redirects to the same folder, but to the server running on port 80. It took me a while to realize what was happening, because there was not wordpress/ directory on the Mac, and it was giving a 404 error. I created that directory, and stuck a simple index.html page in to redirect back to the Ubuntu server. Of course, I got a nice redirect loop going on.

I’m guessing that the wordpress install doesn’t realize that to the outside world, it’s on port 8888, and some script tells it to return port 80, which sends the browser back to the Mac server. I don’t want to run wordpress on the Mac server. Is there any way to set it so that I can run wordpress on my Ubuntu server NAT routed on port 8888?