Had the same experience with the run-flats. Hated them. Was almost ready to get rid of the car. Have had 3 Lexus and this was first unsatisfactory experience. Replaced them with Michelin Pilots and can't believe the improvement. Handling, ride and noise dramatic improvement. Am now a happy camper.
Prestone makes a kit that contains an inflator and sealer. I purchased one ($28) and carry it in the trunk in the event of a flat. This is pretty much the same system that BMW provides with their M series cars which come standard without a spare and have regular tires, not run-flats. Figure if it is good enopugh for them it's good enough for me. Lexus should follow suit instead of having unhappy drivers.