Sure, you can add a button for anything with JQM. Just create a button, and set the text to "Near My Location"...
There's nothing in JQM to help you find your nearest local office, though.
You can use the HTML5 geolocation API on those devices that support it to obtain the latitude/longitude of the user''s location. It's then up to you to implement a web service or web page on your server that you can use to provide the nearest office location, given coordinates.