I had the dealership near me do a full flush using the Toyota WS fluid. It wasn't too cheap, around $250 IIRC. They end up using a machine to exchange a full 12-16 quarts of fluid.
Based on the link in Post # 4, it seems some people had luck just doing a few drain-and-fills using the Toyota WS fluid. This might be a cheaper alternative to the dealership, but it won't get the fluid out of the torque converter, where I believe the problem is actually occurring.
Also it is possible to do the full fluid exchange yourself by pulling the return line at the radiator. Basically you pull the line, turn the car on so it pumps out a couple quarts, shut it off, fill with a couple of quarts, and repeat until fresh fluid starts to come out.
If you do it yourself using one of the two methods above, keep in mind that you will have to do a final check of the fluid level at operating temperature.