Power Gating a Comparator
Here is an idea, based on your existing  circuit. Basically, you need to modify the circuit so that all pathways to GND are cut off by the NMOS. See below. I think this may work, but I really can't say I recommend it. It would be so much easier to find a component with an acceptable quiescent current, or a shutdown pin. Also, if you do this, you need to make sure that the output of the comparator has no path to GND. It is OK if the output is pulled up to VDD, or is floating (connected to CMOS input of a powered up device), but there cannot be any type of pulldown or anything that will sink current to GND.