Out of curiosity, what's the driving force behind the request? Is it to limit the projects that show up on the timecard? If yes, those tasks should fall off the timecard once the timeframe for the task is finished. Unless the end users are pinning tasks to their timecard. Those would need to be manually removed.
One quick way that you might review this is to change the grouping on the project to show:
- Owner: Job Role
- Owner: Name
This will group the tasks first by Job Role and then by the user assigned, so you could see on the Standard view the relevant data.
Generally speaking though for our use case, we would keep those users and job roles assigned from a historical perspective when reviewing things like time to complete, and user capacity.