Nothing you could pour on the CPU, or attach to the RAM or GPU as a conductor of heat is going to keep all three fans from spinning. It's a heat box, so the most you'll get out of the effect is a drop in temperature (which is very good), but the fans still want to run
I believe applications like FANGUI will let you look at temps, and the results of gameplay usage, and also allow you to alter the way fans spin by throttling them down, but these are temporary effects, as intense graphic usage requires constant cooling. Maybe one of the other guys with FANGUI experience can shed some more light.
The CPU already has a conductive material between the CPU and the heatsink, and yes, you will void the warranty if you open up the laptop and modify the mateiral by cleaning and then reapplying new Arctic Silver to the CPU and heatsink. The only places you won't void Dell warranties are the RAM, adding an internal bluetooth card, changing the battery, and physically cleaning the fans. Which you should consider doing if you've had it for awhile and fans seem noisier than usual. That makes the biggest difference.
The biggest GPU tweak would be to download the Omega drivers, which come with Radlinker, and use the Radlinker application to overclock the card a bit. That'll get you a little performance boost, but you'll still have heat and fans.