Questions Dynamic Selectors for Projects

Has anyone built or have experience with building dynamic selectors on Timesheets, Expense Reports, AP transactions?  Specifically, looking to limit selection items (Labor, Expenses, NonStock, and Stock) that are budgeted (either revenue or cost) on a Project and Task.

This behavior was recently added to Cost Codes, in which the selector column filter was added to only include cost codes budgeted on the project task.  The selector code that is used, that we can't seem to find to analyze is a data field called IsProjectOverride and called Used in Project.  Would love mirror this code for Items too.