Degreaser then lubricant
I couldn't get the bushing off either. I put my entire odometer on the spindle with the bushings in a ziplock bag and filled with Oranj Peelz degreaser to cover. After maybe 4 hours soaking or half a day, I took it out and starting working the numbered dials back and forth to break up the crud in between them and let the degreaser get to more surface area. I put it back in the ziplock, resoaked the odometer again in Oranj Peelz for another 4-8 hours, took it out, let it air dry some, and then used light lubricant. I then set the odometer to 9999.9 or something like that to test the odometer when all the gears would be at their greatest load. I figure if the Odometer was loosened and lubricated enough to turn all the gears at once, it'd be good enough to use again.
I have done this to two separate odometer spindles with the bushing. The first one I did I didn't soak, twist, and soak nearly enough, and my resulting odometer still skipped. The second one I did worked fine. I haven't had cause to go back to the first one and try again, so I'd recommend really being patient and soaking / twisting / soaking over and over again until every single number is very very easy to spin.
I've got about 200 miles on the odometer since the degrease / lube and it's been fine. I don't believe my degrease and lube was as thorough as it would have been if I had disassembled, so I could run into problems quicker than others who did the complete cleaning with the bushing off. Also, I'm a little worried that because I didn't disassemble, I was not able to get the the odometer assembly completely dry, and I'm not sure if this method will promote rust in the future and really ruin the odometer.
Finally, I should warn you, I am a relative FJ40 noob -- so take my advice with a grain of salt.
Good luck. If you decide to go this route and have any success or difficulties, please post them up.