I'm not sure how exactly to do it code wise, but I know it is possible to do as we have that at work. I can't access it while I'm at home, but I could try and take a look at the code on the page to see how it's done sometime next week.
For something I see so often, I can't understand why there are nobody seems to be explain how to do it. I need it again, and I'm going to figure it out this time so I'll be sure to post it here when I do.
Mac OS 10.6.7 - Personal Ubuntu Server 11.04 - Server