the sort of thing you are looking for?
http://www.abtelectronics.com/scripts/site/site_product.php3?id=2772
Tad expensive but a google search on simmer plates brings up quite a few variants, we even have a cheap multi perforated version in our local hardware store for ordinary gas hobs.
Didn't the grill plate from Index work which you posted pictures of previously, or doesn't it get up to temp. Will probably look at aquiring an index one as they appear to work really well.. can't go wrong at that price.
Simes