Bring cream cheese to room temperature and whip together with milk, lime or lemon juice, and vanilla. pour into pie shell, top with cool whip or whipped cream and chill.
Alternatively, fold the cool whip into the pie filling and then spoon into shell and chill.
We usually leave the cool whip/cream out entirely and freeze the pie.
Also, you can make your own sweetened condensed milk. I used turbinado sugar to make mine, which made me feel better about serving this to my pie-loving toddler.