LINQ runtime OrderBy

I have a List<MyObjecT> that I would like to be able to sort at run-time. I wanto to do this, without the giant IF statement
 

  private List<Customer> SortCustomer(string sortBy, string sortOrder) 
  {
     // obviously I get this from a service in the real code
     var myList = new List<Customer>(); 
    
     if (sortBy == "firstname" && sortOrder == "asc") {
         return myList.OrderBy(x => x.FirstName);
     } else if (sortBy == "firstname" && sortOrder == "desc") {
         return myList.OrderByDesc(x => x.firstName);
     } else if ..... // you get the idea

  }

 
I can't sort in the database easily (one of the fields is a decimal stored as string, another is a lookup field, but there's no lookup table so in the database it is just an int field with no reference. I didn't want to deal with trying to convert the db fields as necessary to sort.
 
I also can't use the Dynamic Linq Library, just to make things more complicated.
 
Any ideas?
 
Thanks,
Andrew