That would be great for all users that wanted a mod flashed, unfortunately AMI security in conjunction with OEM security do all their efforts, not to support this.
So what you may find around is ways to bypass/trick the system, in this case the offline by USB BFB was one of those, primarily.
You may try using FPT tool if FD is unlock or if it can be unlocked or finally, using an SPI IC programmer.
All my current and past ASUS mbs, all with USB BFB, were successful flashed with mods, using this feature, all the fail mods were also recovered to a working state, suing original bios files, also with this feature.
Good luck and you may wait for other users contributions.