Back then before FW 2.5X we were happily using PS3Proxy to redirect packages of full games and old demos to our PS3s. As time progressed these holes were patched and we just get an error message. But there's an alternative to a proxy.
What if we did DNS redirection. The PS3 (what I think) checks to see if the package downloaded from where-ever it came from is from PSN and has the corresponding name. What if we set up an internal "us.psn.." inside a home network and enable it when we're switching. If the DNS is the same as the Sony url and so is the file then it should install. Sounds logical?