Without trying it yet (I'm aiming for a similar setup in the future): it should be possible to create an MD device with mdadm --build, which should just create a plain raid without any kind of superblock - see the man page for details. I would strongly suggest trying out first on a couple of loop devices (see man losetup) to make sure it works: put two or more loop devices in an MD RAID and keep two copies of the initial content for reference, do arbitrary data changes to the MD and one reference copy, disassemble the MD device, compare the MD members and the reference copy. Repeat a reasonable number of times. If it fails, compare with the untouched reference to see where are the differences and submit a bug report.
