I took my long time buddy who's a toyota mechanic for a ride last night and of course I couldn't simulate the problem. Figures.

 

I would say the only thing left is shocks. Unless you want to try rebalancing the tires. See if he can recalibrate the balancer first. I don't think it is the drive shaft as it would give more of a buzzing type of vibration, nothing that should cause a rear end hopping thing. Not trying to start a fight, but yes a shaft vibration will come and go just like a tire vibration.

 

Its not the tires/wheels. I'm positive of that