Assuming you're using the WiebeTech 3112 flasher, try this kext in place of the bundled one. I did the patch I described. No guarantees, but it should get further than it currently does...

I'm assuming you will put the firmware you're trying to flash in place of the WiebeSATA3112.bin file...no idea if the stock WiebeTech firmware will work by itself.

WiebeSATA3112Flash.kext.zip