I supposed it could be done with a naturally aspirated engine, but you wouldn't gain as much from the intercooling, and there'd be a long way for the air to go in between the air filter and the engine itself, making the engine work harder to get its air (to the point where it would probably negate the cooler air).

A turbo or a blower pushes the air through the intercooler on the way to the engine, and even in this case, some boost is lost simply 'cause of the distance travelled. This is counteracted by the cooler air, allowing more fuel to be used without drastically raising EGT's.

In short, I think you could intercool the engine (although you might risk starving the engine of air), but there's no real point to it.

I hope I was able to explain myself well enough...I'm dead-tired; chances are all I just typed up there is gibberish that I'll have to edit tomorrow...