I wouldn't know one way or another if this is possible or not, that being said, with all logistics of making the mod set aside momentarily, I'd imagine a "simple" ( read: not intricately complex ) solution would be to attach some sort of morale penalty to any units not immune to morale shock that are within a certain distance of a routing unit; I'm sure it could even be designed so the effect intensifies the closer the unit is.
It would create an interesting twist on the rout system. If the unit right next to you falls apart, witnessing the chaos up close would have a profound effect, as opposed to a unit on the other side of the line, less so on a unit held back for reinforcements, so on and so forth. ( Also, the routing units that stray close to units held back could effect units by the sight ( a.k.a. proximity ) of the fleeing unit; First thing I think of is how reinforcing soldiers first site on arrival are the wounded and broken being taken off the field they are marching onto, would produce some sort of negative impact on morale, not enough to make the unit flee outright, and the effect would pass before/during being thrown into the thick of it. )
On paper it sounds amazing

it could create a new emphasis on morale shocks, actually having to know which enemy units are vulnerable, and timing when to focus anything morale breaking at the perfect spot to create that cascading rout effect. At the same time, if a group of light infantry that are directly near a unit of your disciplined front line, while effected by witnessing the battered unit fleeing, once the unit is gone, they are refocused on the task at hand. Utilize this, and tweak the Army Losses effect to compensate for anything needing to be compensated, and ta-da. See, simple.
