Hi zakman,
Maybe you have a possibility to add a plastic screw (or metal screw), if you have this hole screw:
The motherboard will at least be stable.
She will not have tendency to fall,
when you put the graphics card.
Otherwise, I put a pieces of (styrofoam) polystyrene food tray isolated, for help keep stable.
Normaly a shop have possibility to give few screw... free cost.
The most important thing is to have
no metal contact between the motherboard and the bottom of the case.Me I use a red washer or white plastic washer under (back side) and front side on the motherboard. This is my personal decision.
Gloup_Gloup