I'm cross posting this here, but I'm not sure if this'll work or not. PROCEED AT YOUR OWN RISK!!
You can load your BIOS file with Award BIOS Editor, found here:
On the latest version of the GA-MA790X-UD4P BIOS the AGESA segment is found as "AGESACPU.ROM", type ID 4067, Size 36867 bytes, fixed offset 00000000.
Now, open the GA-MA790XT-UD4P BIOS (with Thuban support) with the BIOS editor. Extract this same file ("AGESACPU.ROM") to the directory you're working in.
Open the GA-MA790X-UD4P BIOS again. Replace the "AGESACPU.ROM" segment with the one extracted from the GA-MA790XT-UD4P BIOS.
Flash the modded BIOS... But I have no idea if this will actually fix things or not, I'm just crossing my fingers that the only thing that needs to be updated is for the CPU to be recognized by its code.
Here is a sample of the modded F9 MA-790X-UD4P BIOS that I just described making
F9m MA-790X-UD4P BIOS
I still don't have my new CPU yet so I'll fiddle with this when it gets here... The dual BIOS feature for these boards should keep you from bricking them, but I can't be responsible if you somehow do!
edit: Just tested this out and the BIOS seems to fail when it does the size checks. Maybe there's some workaround with another program like MM.Edited by test tube - 4/27/10 at 12:42pm