Is it possible to install a whole house humidifier away from the furnace?
I suggest a swamp cooler - or as Home Depot calls them online 'Portable Evaporative Cooler.'

The big ones (which do come with wheels), a seem to do well in the reviews. There are many negative ones, but those seem mostly from people who do not understand what the product does. The are listed under the Air Conditioning heading, and talk about how much cooler they will make the room.

But you will not sell many with a slogan of 'These things toss water in the air, hope it sticks to you, and when the hot air, with no humidity from outside hits you, it will evaporate off your skin, and you will feel cooler'.

However, if your goal is to have humidity - even most of the negative reviews will sound good to you.