Using liquid metal on the stock IHS won't really net you much benefit if at all. Most people that use liquid metal use it after they remove the IHS from their CPU with a delidding tool. They use it to replace the stock indium based alloy they use to bond the IHS to the CPU die. Doing so lets them remove more material as the solder is thicker thus making the heat have less distance to travel through. After you remove the IHS you then have to remove the solder from the CPU die and the bottom of the IHS (unless you intend to do direct die cooler mounting) as well as remove the adhesive that held the IHS on. 
 
It's a whole process but most people will then sand the IHS flat as most CPU IHS are concave and then they will apply the liquid metal directly to the CPU die and then reattach the IHS. They reattach the IHS because if not it lowers the CPU Z axis height and makes mounting a cooler far more difficult and will require custom modification to your coolers mounting hardware or the CPUs retention bracket in order to actually contact the CPU without the IHS. 
 
TL:DR, no don't bother with liquid metal unless you intend to do it properly.