You know initfs_flasher starts from the existing initfs, not from it's own image? It then adds and removes stuff from there. I'm trying to recover my SD boot now, so I'm not flashing Diablo yet, or I'd try. But I'm pretty sure it should work with at most minimal modifications. And you can always remount the initfs read-write, and just modify it yourself... It's not that hard, once there's enough free space to be writable.