Hello @Beckie Ryan ,
I think the best way to accomplish this is to set up a custom Billing Rate Level that you will only use with this employee. Within that item, you can choose Custom Hourly Rate per Service Item and proceed to set up custom rates for the service items that you check off.
Then you would go to that Employee and assign this Billing Level Name to that employee.
Note that this simply overrides the standard billing rate that you have already set up in the Service item on the Item list, which I think is what you want. Any other service items that you want to set-up specifically for this employee you can add at any time. Then you would just go into the Billing Rate Level list and edit the list for Employee A to include any new items, make changes, or exclude older items.
Hope that helps :)