If I buy a basic spec iQ1, can I, at a later date, retro-fit the TNS510 Sat-Nav? Or do I HAVE TO buy it as an option at the same time as I buy the car new? (If I want one that is) Ideally, I would like to buy an iQ and add the Sat-Nav to it at a later date. Just wondering if it can be done! Cheers, jasonjalet