My take on this is simple...
When you shutdown your pc the cooling system stops too, but you still have that loop passively cooling the components as heat dissipates into the almost motionless water.
I only have to question why the heck this would actually benefit you?
Consider that all the stock and air cooled systems out there immediately have their fans stop once the PC shuts down.
All they have now is a passive heat sink and I am willing to bet that our loops have much more ability to handle that minute amount of heat from power down under load than a dinky Intel stock cooler.
Hey, if you want to set it up for the hell of it, we won't stop you, and many above have provided great input on how to accomplish this.
Just know that for the sake of making it known...this will not prolong the life of your chip. They are designed this way...
Think of a car cooling system which runs a heck of a lot hotter...those electric/thermostat driven fans only continue to spin after you shut the car off once in awhile on a super hot day.
That is on newer cars...My old ass 91 Jimmy has a direct drive fan and it only spins when the engine is cranking away. I never overheat, nor have I had any issues with overheating.
Plus an engine block sure as heck does not dissipate heat as quickly as some small micro chip that has a dedicated loop on it.