What facilities do you have for accessing other media types on your ps2?
Easiest way would be to copy the save from the ps3 to a USB flash drive then using a ps2 exploit to load it from the USB flash when you get home.
The one way thing kinda sucks if that is true.
Maybe if your brother has linux installed there may be other options.. Has anyone tried to mount the USB memcard adapter as a r/w filesystem device in Yellow Dog? can you even see it as a hardware device?
I am sorry I cannot offer much more help than thought fodder.
...If it is in memory it can be touched...