I too am wondering about this, being in a northern clime and having just acquired a new guitar.

The info with the new instrument seems to offer caution on both sides -- saying not to put anything wet in your sound hole unless it's really needed, and then saying it is certainly needed if the humidity dips to 50%, which seems extremely unlikely here.

When I check the local weather page on my computer it's usually in the 85% range. I've decided to trust to a room humidifier to keep the house air at the right humidity and hope this will satisfy the requirements. I'm really leary of placing a water wick (so to speak) into an instrument.