At least in my case, if you tried that the bolt end would hit the firewall; remember, in order to have a few threads showing, that end will stick out farther than the head of the bolt. In fact, with mine, there wouldn't even be clearance for just the bolt head without the hole in the firewall. Certainly no way to get a wrench in there and tighten it.
It really isn't much trouble to make that hole, and would probably be more effort to effectively torque that nut even if you could manage to get it in place.
Chris