So, I was a bit bored today, so I figured out how the .pack format is laid out.
https://gist.github.com/169c657b091bf356f7fd
and here is an unpacker tool:
https://dl.dropbox.com/u/1940586/ps2unpacker.zip
Source is in the zip. The source is pretty terrible, but it works. There is also an unpackall script that crashes the tool on the first iteration. Just hit 'Close this program' when it pops up and it will keep working.