CJ,
You don't need to buy a $30.00 tool. A vise grip and a large flat screw driver will do the trick.
Poke the hole through the welt.
Insert the rivet. Catch the underside edge of the of the grill with the vise grip (use some padding if freshly painted) and with leverage, press the rivet top with the othe jaw of the vise grip.
Hold this position while you use a large standard screw diver to spread the rivet open as much as you can. Once the rivet is slightly spread, use the vise grip to finish the crimp.
I had a freshly painted grill. Not wanting to scratch it up, I brought it inside, set up on a carpet and a blanket for extra protection.
It's a little tricky, but once you get the routine down, it will go pretty quick.
Tim