I followed these 2 steps to create my persistent file.
This gave me an 800Mb file that I placed at the root of a FAT32 partition. I did put it in a different partition then the casper directory, but I don't think that that makes a difference. I wanted it in a separate partition that i could manipulate while booted in BT4 non-persistent or Windows. This has worked fine and is detected at boot.Code:dd if=/dev/zero of=casper-rw bs=1M count=800 mkfs.ext3 -F casper-rw