I had to do that for my own version, storing a new field for salesmen which could waiter as well. Unfortunatley I did not find out how to bring it to the ticket in the ticket edit panel. But I agree, this should be stored, because the cashier can be diferent from the waiter.
example picture would be good to understand your real requirements
Add Filters for "Products by location"-screen
Write originalUser() to ticket table for sales analisis