I don't know who is reading this anymore but I wanted to check a possible solution. What if I put silicone around the rim of the manifold and let it dry so that when I put it on it would create a sort of gasket. I also want to let it dry on the manifold in case it doesnt work, I can scrape it off. I don't want to have to scrape the grill as well.
My only concern would be the grilling heat, but it may not get too hot below the coals.
But the last thing I want to do is cap the current hole and drill another. I don't want to turn my grill into swiss cheese.