Wouldn't it be possible to downgrade a PS3 using PS3 ProxyServer GUI, a modified version ps3-update.txt, and replacing the updated firmware link with the firmware that you want to downgrade?
I'm currently on 2.41, and if I say that the latest firmware is 3.00, the PS3 will then request that I download the latest firmware, which is actually is version 1.10. Won't that work? This is just a thought.
The PS3 checks what FW version you are running therefore if you are running 2.41 and try to downgrade to 1.00 it won't allow you. Once you modify a PS3 update to make it think its a higher update version when its really lower doesn't work either because as soon as you do it you will break the signature on the update.