Another alternative is to do what I did....

I moked up a template out of cardboard that utilizes the umbrella holder screw connections as the support, took it to my local plastics shop and had then cut me a smoked piece of 1/4 inch lexan with rounded edges.

I had to spend some time with wet sandpaper to get the edges nice and smooth (just a tad on the OCD side!! - or is that CDO for the correct alphabetical order ;-))

$60.00 Canadian.

Looks great, works awesome.