Asus Crosshair IV extreme - 4g decoding enable ?

Hello, asus crosshair IV extreme don't have the 4g decoding option in bios, and you need it to use more than 3 GPUS in the same mobo, without it, windows wont detect more than 3 gpu, even with the board having 5 pci-e slots.

Is it possible to mod the bios to enable 4g decoding ?

PICEX to Gen1 or Gen2 is useful also.

Original bios: http://www.asus.com/Motherboards/CROSSHA...pDesk_CPU/