Unfortunately it's not possible, BUT since these are overhead tasks/assigned to many users as you said, could you work around that by simply putting a short description in the task NAME? Since these seem to always live as pinned tasks in timesheets, and there is a lot of real estate still with the task name column, I'd leverage this to add in a brief description or at least the task name a little more descriptive for users to know which to add hours to that way. Just a thought!
If this helped you, please mark correct to help others : )