You'll need
1/2" electrical conduit
1/2" conduit straps
Screws for straps
Two pieces of wood 13"x24" depending on your grill size and table size desires

Step 1: The Assembly.

The pictures say 1000 words. Trace the lid of grill on to your wood to get your curve. Mine was about 22". Weber does make smaller grills. I bisected two pieces of wood together to make my 13" x 24" side tables. 1/2" electrical conduit and straps are used to assemble as shown. It becomes adjustable if you want to slide the wood along the conduit. The straps along the curve fix it to the grill.

Step 2: Installation

Position one of the tables centered over the grill handle as shown. This is a picture from underneath. I used two more straps to secure it so I can lift the table to move the grill. Adjust the wood along the conduit until the lid will close and seal. You might need to re trim the wood a little to get a factory fit.