Still not working... Now I'm a little confused about this whole boot.efi thing.
Since I'm running with Tiamo's script my ioreg says "EFI64".
...I've replaced the boot.efi on the USB drive at both places. Did I need to do that at all?
(I still get the not to possible to install message)
here's a really nice guide about how to create a USB installer ->
https://forums.macrumors.com/posts/20075605/