Forum OpenACS Q&A: Re: openacs server behind the firewall
You can start rooting around in packages/acs-admin/www/install/index.tcl to set the repository location.
Lars might pipe-in if you're interested in doing something like this. I'm sure you're not the only one affected by lack of proxy capacity in aolserver. Lots of folks with oacs 5.x servers will be behind firewals, so this would probably be a good general solution.