I use FUJIK thermal glue. It's cheap (DX has it), and it works decently. I save my Arctic Alumina and nicer thermal adhesives for LED stars.
You just want to slather the stuff on there to give it less contact with air and give it more thermal paths to the pill. If you can add extra thermal mass in the pill such a copper washer or something like that in some of the space between the pill and driver, it would help heatsinking even more. If you're using a 7135 based linear regulating driver, then it's mostly important to pot those on the sides to the pill, as they are the main source of heat usually. Also, I would try the copper foil / foil tape mod to ensure that there is thermal transfer from the pill to the body of the light.
