In Joomla 1.6, this happens naturally for a lot of the fields.. it's a bonus of the newer system. There should be a few ways to do this, but will have to investigate a bit. Let me know how the JomSocial profile plugin file I sent you works, and I can likely send you a few lines of code to add to that which will hopefully do what you're looking for.
Definitely agree that this is something that will need to go in a future release and have added it to our bug tracker.
Thanks,
Alex