[REQUEST] Guide to sign existing GPU Bios with my own Secureboot Keys

hi

is there a guide to mod an GPU Bios file with my own secureboot keys?
i am using my system with my own keys for secureboot already but i have to trust the microsoft keys for the (gpu)roms in the system
if i could add a signature from my own keys to the gpu bios i could switch to using my keys only.

best would be to have both signatures on the same time

thanks