For those with Linux boxes, it should be fairly trivial.

I'm working on getting RAID1 working and it looks like the only way to make it work will be to modify the initrd filesystem, which means I'll have to make a new .upgrade, as I'm not aware of any other facility for uploading it, as it resides in flash (I think).

So once I get that working, I'll let you know some specific steps. However, you should be able to use Sven's UpgradeSplitterBuilder to generate one (although I haven't gotten to the point of actually trying yet). Read the man page for losetup and the ``-o loop'' parts of the man page for mount for some more information about generating the filesystem image.