It can be done.
I just finished mine, a bit of work and creativity but quite easy and very do-able with a few tools and a bit of metal for some brackets.
The key to this is the info that the Nautilus comes apart into two pieces, the horn and the compressor. There is a little tab at the top, break it and they will easily slide apart.
The compressor fits quite nicely under the windshield, that's an easy one. Remove the two mirrors and slide the shield back. You will see a nice empty spot for the compressor...I mounted mine with a small bracket to the allen bole that holds the ground wire to the instument cluster - also a good place to ground the compressor negative wire.
The relay I mounted to the old horn bracket, just bolted right on. I ran a power wire right from the battery (with a fuse holder inline!!!) to the relay, under the side of the tank. The only place you can see the wire is where it goes over the top of the frame at the front of the tank, but running it in another location is a longer project for next time.
The horn itself I mounted on the left side of the engine, just behind the fairing. I bent a bracket to mount on the fan bracket bolt and screwed it inti the horn.
Get a piece of tubing from your local hardware store, I got two feet, $1.25 total.
Run the tubing from the compressor to the horn, wire everything up according to the Stebel instructions and plug your ears!