You could grab the ospack, use romburst to extract the initrd.bin, then mount it as as cramfs... that's what I tend to do (though I'm using Windows atm and don't have a copy handy)
I'd be interested to see what you can do, as when I tried (with OZ3.2 iirc), I eventually ended up (after adding a long list of required libs - hence the mounting the fs so I could easily copy them) with an undefined symbols error and gave up in disgust (I wasn't overly motivated though ;-).
Si