Something

#!/bin/sh

PATH=/sbin:/bin

MODULE="$1"
shift

if [ "$MODULE" = "nvidia" ]; then
	if [ -e /lib/linux-restricted-modules/.nvidia_legacy_installed ]; then
		MODULE="nvidia_legacy"
	fi
	if [ -e /lib/linux-restricted-modules/.nvidia_new_installed ]; then
		MODULE="nvidia_new"
	fi
	XORG="nvidia";
elif [ "$MODULE" = "nvidia_legacy" -o "$MODULE" = "nvidia_new" ]; then
	XORG="nvidia";
elif [ "$MODULE" = "fglrx" ]; then
	XORG="fglrx";
fi

if cat /etc/X11/xorg.conf 2>/dev/null | \
  sed -n -e '/^[ \t]*section[ \\t]*"device"/I,/^[ \t]*endsection/I{/^[ \t]*driver[ \t]*/I{s/^[ \t]*driver[ \t]*"*//I;s/"*[ \t]*$//;p}}' | \
  grep -q -w $XORG; then
	modprobe --ignore-install -Qb $@ $MODULE
else
	echo "Not loading $MODULE module; not used in /etc/X11/xorg.conf" 1>&2
fi