List.Sort by property name - Including subclasses

I have a bit of a challenge. I need to sort a List of objects, and I need to sort it from a string representing the path to the property in any sub class. I need to use the List.Sort() and not OrderBy().

Lest make a simple example. I have a list of persons represented by two sub classes for identification and name

public class NameParts
{
    public String FirstName { get; set; }
    public String LastName { get; set; }
}

public class Identification
{
    public String NiNumber { get; set; }
    public NameParts Name { get; set; }
}

public class Person
{
    public String Email { get; set; }
    public String Phone { get; set; }
    public Int16 Age { get; set; }

    public Identification Id { get; set; }
}

Now I need to sort the list by age. Very simple

 public static void SortByAge(List<Person> listToSort)
 {
     listToSort.Sort((x, y) => x.Age.CompareTo(y.Age));
 }

And even by NiNumber and FirstName it is fairly simple this way

 public static void SortByNiNumber(List<Person> listToSort)
 {
      listToSort.Sort((x, y) => x.Id.NiNumber.CompareTo(y.Id.NiNumber));
 }

 public static void SortByFirstName(List<Person> listToSort)
 {
      listToSort.Sort((x, y) => x.Id.Name.FirstName.CompareTo(y.Id.Name.FirstName));
 }

Now comes the tricky part. I need to perform all the above sorts giving a string that represents the path to theproperty to sort by. Like "Id.Name.FirstName"

So I need

 public static void SortByAny(List<Person> listToSort, String sortBy)
 {
   //??????
 }

That can be called with

 List<Person> theList = new List<Person>();
 SortByAny(theList, "Age");
 SortByAny(theList, "Id.NiNumber");
 SortByAny(theList, "Id.Name.FirstName");

I know I need to use reflection for this, and I have managed to do so but I cannot get further than properties in the Person Class itself, so I probably need to do something else, and this is where I'm stuck.

Does anyone have some brilliant ideas on how to solve this?

Thanks