Just spray some water to surface of it, when water vaporizes it cools down surface and surrounding air, making cooler colder and then it cools compressed air inside of it better. Obviously works best with air/air coolers
Also spraying water to compressed air is decreasing temp dramatically, but problem with that is that some of water tends to get to intercooler, slowly filling it, also there will be some condensing to worry about.
And yes, you can spray water to engine, that is how you can also clean engine, however I won't recommend anyone to try without some training or learning, it is possible to destroy engine with this too.
But if someone needs to find ways how to cool intercooler, then he has just too small installed