HELP - 5D mark III quick buttons flash function settings

Hi,

I need a bit of help here from 5Dmk3 owners. I have 1.2.3 firmware in my mk3 and am so curious as to is there change in later firmwares to allow flash function settings to be assigned to custom controls. I was able to set it to set button and was quickly accessible to me when ever i needed it. It was available on 5Dmk2 and is available on 5Dmk4, but i cant seem to find it on 5Dmk3.

Please help guys.