I think I am confused by your question.
A NEMA box is just a weather resistant box.
I'm not sure what prompted you to think that we are running AC power up the mast, but as you said, that is rare (we don't do it). When a device doesn't support PoE, such as the WRT54G, we can still use the unused pairs of Cat5 cable to power it.
The simple explanation is that you use the unused pairs to carry the 12v from the device's original power supply. It isn't true PoE, but it works up to a distance.
Here is a link to a product that can provide PoE power to a non-PoE device. The one thing that you can't see in the picture is the device end that has the barrel connector to provide power to the device.
P.S. To the original poster, I'm in VA now and heading out in the morning (Sunday). If you want me to stop by and take a look at your situation, I would be more than happy to do it. I'm not looking for payment so don't worry, I'm not trying to hustle you. :) If you want to chat, you can email me at gene at my handle dot com.