If I understand what you are describing, all models (Toyota & Lexus) have it. I use the same way, find its not always correct. There are situation where the engine kicks in earlier, but usually that is due to cold weather driving and wouldn't usually have much effect on a long highway cruise.

The 42mph rule must not be completely true, as I definaly have been electric only as speeds as high as 60 to 65, but only when coasting downhill without any power applied. If I touch the throttle at all, the engine does spring back to life.

The technique you are describing could just as easily be done with your foot, and might actually be more effective as you can keep pumping in just enough power to maximize the run times with ICE (internal combustion engine). Howeve I have to say using the cruise control is often easier, especially if you are going to be doing it over a period of hours.

The actual technique you are describing is usually called P&G or Pulse and Gluide. If you like that sort of thing, you might want to check out http://www.cleanmpg.com; They are a hypermiling site not specific to hybrid vehicles, but the information can be applied and they do have a lot of hybrid users. You can find me there under the same id. The primary guy there is Wayne and he gets some very impressive mileage and does a lot to promote hypermiling techniques which can range from the simple "accelerate slowly and don't speed", to mechanical, "inflate tires to max sidewall pressure" to advanced techniques which may involve manually shutting off ICE when not needed and long distance coasting. I only do a few things from there, but it really helped my mileage.

And I agree, these cars love to roll. I think the Lexas has an advantage. I think it comes with some preety good low-rolling resistance tires.

Have fun,
Jonathan