I don't think you can automate what you'd like to do.  We have only one person like this and do it like this:  After entering time, we use Task - Enter Checks - Click on Taxes - choose the resident state from the list - and type in the amount they want withheld each pay period.  Then we reprocess all checks.  It works. 

That is what we are doing now.  Pain in the rear when you have so many employees that you are processing each week.