You can change the sort order in the script of the employees. Create a small table that loads the employees sorted in the order you want. That will determine the load order of the employees. Once you done that you can load the other data and finally drop the table you created to sort the employees. Then you can sort the chart by Y-value and the employees will be sorted by their load order in the order you defined in the script.
If you don't want to change the script you will have to get quite creative with the Ord function on the first N characters to create a numeric value that indicates a sort order.