Adding USB 3 media module to Latitude E6520

i saw in some literature that the E6520 can have USB 3 media modules installed.  Here is what it said: "A variety of long battery life options, including ExpressCharge™ battery options, and swappable media module options, including optical drives, hard drive and USB 3.0 media module options, help to keep productivity in full swing."  Is this something that can be done to my current laptop or is that something that has to be installed initially when it is built?  I'd prefer USB 3 for use with a SSD external drive I recently purchased.  Thanks for any answers.