When you create a unit u have a placement radius option, increase that and the dude will be placed in a different spot within that radius each time. Also, when u give him waypoints for patroling u can increase the waypoints placement radius too making dude take a slightly different route each time.
U should also check out the 'Probability of presence' slider on the create unit box. If this is set to 50% the unit will only be on the map half the time. For example, in a mission i have just made, when the team gets to a town a BMP and 5 infantry, set on a 75% probability of presence, come down out of the forest to the north....but i have set another BMP and another 5 men, on a 25% prob of pres, to come from the east. So most of the time u just get the squad from the north, sometimes one from the east and every now and then u get both ;D
Happy editing :thumbsup: