arch-desktop/install/etc/polkit-1/rules.d/00-mount-internal.rules

polkit.addRule(function(action, subject) {
	if ((action.id == "org.freedesktop.udisks2.filesystem-mount-system" && subject.local && subject.active && subject.isInGroup("storage")))
	{
		return polkit.Result.YES;
	}
});