If you Google it, there is a company called Kettle Pizza that makes a topper attachment for Weber and other kettle style grills.
http://www.kettlepizza.com/?gclid=CMLF_oKr08cCFQtFaQodop0I_Q
The grill topper is made of stainless steel and it creates a tall ring that goes in between the bottom of the kettle and the lid. It adds about a foot of height to the grill and has an opening in front where you slide the pizza in and out. You use regular charcoal briquettes and hardwood charcoal together. With this extra height, and the combination of charcoal, now the heat really wratchets up into the brick oven range. You can get up to 750 degrees or more in your regular Weber grill.
Kettle Pizza isn't the only one making these. If you Google it, there are some other attachments you can get.