[rt-users] populate other custom fields from autocomplete custom field

[jiten]

I have three custom fields:
1. Employee name (automcomplete)
2. Employee id (not visible to users)
3. Business unit

The users will type in the employee name partially and get suggestions and
complete the name using the suggestions. I have this part working.

I understand that I will have to customize the code and am happy to do
that.
What I want to make happen is that the employee id and business unit of
that employee be automatically set when employee is selected. What is the
best approach for this and what files would I need to modify?