I've been wondering about something quite similar! In most, if not all of the tutorials I've read the paint is being applied to the body on the downward stroke, ie. as you're submersing the body. You then have to clear an area in the water in which to remove the body, to avoid applying more unwanted paint. I'm wondering how it would work if you submersed the body first, then put the paint into suspension in the water, and then pulled the body upwards through it, so that the paint is applied as the body leaves the tank.
I think this is basically the same as your second idea?
Gonna have to break out the dipping tank and some wood scraps methinks!
DJ
What i would do...
I should put a screw only on strap button hole of the right side of the body (fitting screw), dive the guitar underwater and leave it alone underwater with a fake neck holding on the side.. (the screw only serves to don't drop the guitar directly on the bottom). Add the color, do the swirl and push the guitar out slowly. Seems very working to me.
Of course you just could call a friend to hold the body when you drop those paints....
I don't like the idea of diveing a guitar body under water, but swirl worth it even if damage. Maybe people dive the body after ad the colours to minimize the time that the body will be under pressure of the water, but a don't think this should a major problem with a well sealed body....