Connecting iPhone 5 to Dual-Band AirPort Express

Now that the iPhone 5 can connect to a Dual-Band 802.11n network, I went out and bought a new AirPort Express that supports broadcasting at both 2.4GHz and 5GHz.  I tested out connecting my iPhone 5 individually to the 2.4GHz network and the 5GHz network I created, and 5GHz seems much faster.

The question is... how do I connect the "Dual-Band" way the iPhone 5 "Features" page talks about?  Does the AirPort Express support connecting to both frequencies at the same time?  I'm fine with connecting to the 5GHz network because it's still plenty fast, but how do I connect the "Dual-Band" way?