hardfile=read-write,32,1,2,512,/dev_usb000/uae/system.hdf
or, if the previous one doesn´t work for you:
hardfile=read-write,0,0,0,512,/dev_usb000/uae/system.hdf

Just in case anyone trys to do it:
you must copy the settings you gave in your winuae for the HDF file. But be aware,
32,1,2,512 dont match the same order then in winuae... in winUAE you have A,B,C,D and in PS3/UAE it's like A,C,B,D or something like that.