There is no secondary ZOC in P&S. They have been added to FoGII "as a way to prevent it being too easy for mobile units to slip through small gaps in the enemy line" :
I do not know if the coding of the secondary ZoC appears in the accessible scripts in the FoGII folder and, if so, to what extent it could be "copied/pasted"/adaptable to the P&S scripts/engine...