MBA -to- ATD - <usb> - External Display?

Hi guys,

At work I have an 11 inch MacBook Air hooked up through thunderbolt to the Thunderbolt display, works great btw.

Anyway, I am looking to hook up another portrait-view monitor on the left of the above setup. I originally tried to hook up a miniDisplayPort to HDMI using the rear Thunderbolt port on the ATD, needless to say this does not work.

So, my question is...can I hook up a USB to VGA/DVI using the USB-out on the back of the ATD to gain the extra monitor capability? Has anyone tried this in the past? Or will I have to use the USB-out on the Macbook Air to achieve this?

The monitor I am trying to hook it up to maxs out at 1080p I think and I will only be using it for code work so performance is not really an issue.

Any help would be greatly appreciated. Also, if anyone can steer me in the right direction in terms of a good USB to VGA/DVI cable (preferably available at Monoprice) that would be great!!

Thanks!!

Sorry I must not have been clear with my question. I have my MacBook Air hooked up to the Thunderbolt display with the included cables. What I am wondering is if I can hook up a USB to DVI/VGA cable to the back of the Thunderbolt display for use as a secondary monitor.

Using a miniDisplay Port to HDMI cable plugged into the back of the Thunderbolt display does not work.

Anybody know? Looking to make the cord purchase this weekend if it will work, just need to make sure if it will if the cord is plugged into the USB on the back of the Thunderbolt display.