This question has been answered by dubbs. See the first response.
I don't thinks so. The extended fields are actually one field containing a JSON array. So you would need to access that array, possibly converting it to a regular array to work with. You could use a snippet to get the extended field and convert it to an array, using the snippet in the getUsers tpl in place of the extended field placeholder.
That's going to be very slow no matter how you do it. You might be better off using BobRay's ClassExtender to create an extended User object. http://bobsguides.com/classextender-class.html