I just did a:

• rootfs+optfs to eMMC using backupmenu-0.65.
• flashed stock RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin
• booted and verified if everything was wiped out
• created a flashable rootfs image from the above rootfs backup using mtd-utils
• extracted the contents of the kernel-power deb by
  Code:

  dpkg -x kernel-power_2.6.28-maemo46_armel.deb

• unpacked the zImage from it using
  Code:

  flasher-3.5 -u -F zImage-2.6.28-maemo46.fiasco

• USB Flashed using
  Code:

  flasher-3.5 -r backupmenu-rootfs.img  -k zImage -f -R

• Restored optfs from above eMMC backup and Im back to where I leftoff in less than 10mins.

w00t! Very cool stuff! Thank you Rob!

PS: I manually downloaded and upgraded my mtd-tools_20100706-1_amd64.deb to mtd-utils_20110107-1_amd64.deb from the Natty repo on my Ubuntu 10.10 before creating the rootfs img.