As the guide say...no.
But, i can tell you to try with your dump, in an alternative way.
1)Patch your dump with flowrebuilder
2)Flashsun with your patched dump, and at the end of operation...DO NOT detach the power cable.
3)Press the red button under the sata cable (reset button) and set the switches 000001
4)Put in your microsd the e3_downgrade.bin file togeter with your dump and press start on e3 flasher
5)At operation finished, detach the power cable and reconnect it, set all switches down.
6)insert your psjailbreak dongle in the right usb port and press start and eject on the ps3
7)If it works, continue with the downgrade operation.