I was looking at doing something like this, but the smallest I could find is M8 and that required drilling the threads out on the seat mounts. I didn’t want want to be that permanent as I tend to be fickle with minor mods. So instead I just got two 90mm long M8 lag bolts with a flanged jamb nut and have them a little more than finger tight. The bags keep the exposed bolt head a little less obvious and the smooth shank protects the seat edge.
Please let us know your steps to install.