Hi Eddie-- I'm anxiously awaiting, but based on some of the Ideas out there (https://community.tableau.com/ideas/2168 ) I don't think this is possible. Please wait until you hear from someone smarter than myself before you give up hope, though.
*Make sure you vote this idea up-- and its duplicates!
If worse comes to worse, with some elbow grease you might be able to calculate it using the USERNAME function. You'd need to know where every potential user is based, and this might change based on Daylight Saving Time or if they happen to drive to another state... so probably more headache than it's worth.
Good luck-- Michael