Squid reverse proxy quandry

[Fpsware]

I've been using Squid Reverse Proxy for a few months and until now everything I've need to do has been pretty easy. I've run into a wall trying to achieve the following:

I want to browse to www.mydomain.co.nz and have it point to the website which is on http://10.10.10.5:81/production_site. At a later date I will need to change the destination to …/production_site2 but that won't have any bearing on my immediate request.

This is what I have so far:
Web Server: 10.10.10.5 Port:81
Mappings: URI www.mydomain.co.nz Peer: [above web server name]
Redirects???

I'm not sure if I've been using redirects incorrectly but when I redirect a site I want the redirection to be invisible to the user. For example if I redirected mysite.mydomain.co.nz to 10.10.10.50/thisthing I don't want the end user to see the 10. address.

Any help would be greatly appreciated.