First off, you can do the secure equivalent of 'rm -rf'. That would wipe out the files, but you wouldn't be able to reboot. Dunno if that's absolutely essential to you, but I don't think it's a good solution anyway.
Second trick might be to try chrooting into a ram disk, and remounting the root partitions within that. I'm fairly sure it wouldn't work though. It's still mounted above, and chroot isn't a full blown 'new' boot. In a similar vein, I wonder if you could use 'kexec' to soft reboot the kernel into a ram disk?
Your best shot might be to reboot and use an initramfs to mount and wipe the SAN filesystems. Although initramfs's are usuually used to load modules and such at bootup, there's not reason you can't have them do anything you want (such as wiping the filesystems). Depending on your distro, there's probably a mkinitramfs package available to help you. Check this
to get the general idea as to what can be achieved.
Finally, it might be easier to try to figure out how to get network booting working rather than messing around with the above. What's the problem with it?
Hope that gives you some ideas.