Another possible solution could arise if the map is ever redrawn. Please note that I am not suggesting the map be redrawn just to solve this problem.
However if the map does get changed at any point I suggest splitting Reims into two separate territories. The northern territory would border Holland and the southern territory would border West Germany and Bavaria. Then you could increase the fortifications for the southern territory. This would seem to be the most elegant solution.
Another idea is to just increase the fortifications in Reims to encourage Germany to go into Holland. As a counter, since not every game should have this, if France falls but Holland was never invaded, Holland becomes a reluctant German ally.
The logic behind this is that Belgium and Holland were too intimidated to enter the war on the Allies side and thus risk fighting the war on their soil. How much more intimidated would they have been with no allies on the continent and the knowledge that Britain could not protect them?
Under such a scenario I would see Germany collecting all of the income and resources for all of Belgium/Holland. This would be detrimental to Japan and could prove interesting.
