Hello Deb,
This is a great advantage in EPM-Project Server 2010 that a PM can see only the fields which are associated to a group. You can set the project for Department & associated custom fields will be visible to PM of same department.
If you are trying to do something similar, create a Project Add in which will have a form for custom fields, You can store your custom field & group mapping in a table in either Repoting database or custom dataabase.
Based on the selection of Group by PM in custom form in project addin, form will get the information from custom db or reporting db using WCF & display the data in form. Now PM can set the fields. Add in will update the same.
Hope that helps.
Thanks,
Amit Khare