If you're just looking for something to create some height, a rotisserie ring will do.
Although the Weber brand one isn't really tight fitting...
The cajun bandit stacker is a magnificent product.
I don't get paid to promote his stuff or anything, but I love the product so much that I feel compelled to recommend it over anything similar.
I've loaned mine out 3 times, and all 3 people that used it fell in love and immediately bought their own.