You could try buying a blank with the transponder in it and then the procedure below. It looks like you have to have power locks and a key fob that locks/unlocks the doors though.
http://www.nissanversaforums.com/how-tos/9017-how-programming-key-fob-tiida-only-not-versa.html
I know the thread title says Tiida only but someone got it to work on a Versa.
http://www.nissanversaforums.com/how-tos/9017-how-programming-key-fob-tiida-only-not-versa.html
I know the thread title says Tiida only but someone got it to work on a Versa.