It won't, I tried that once and the temps were about the same, the only difference was just how much faster it cooled down, which still wasn't by a lot. Stick with thermal paste for the IHS. It's also not a good idea because the gallium in the liquid metal could corrode the copper of your cooler if it uses a copper heat plate, wouldn't be a pretty sight. And to put the cherry on-top as to why it's not a good idea, the seal between the CPU IHS and cooler isn't the best environment to keep the liquid metal in place, especially since your motherboard is most likely vertical. There could be a small chance of liquid metal falling onto your motherboard components and shorting it out.