Milkmandan, you want to use EK Supremes right?
So get rid of the backplates, how are you gonna get the EK mounting screws through them? That's right, you aren't.
Try to mount with the spring clip, if that doesn't work install without anything. Works fine too (that's the way an EK supreme is mounted normally on any mobo, without any backplate)
Just don't tighten it too much, but it doesn't need high force anyway. Never made a difference for me, slight pressure is enough,