What about using a step up transformer to send 240V to your panel from the 120V output from some EVs?

This whole approach has an excellent chance of working extremely poorly. A device intended to power a whole house will have the ability to supply someone’s idea of the inrush current needed by a house, the reactive and harmonic current needed by a house, and the quality of waveform needed by a house. An EV’s 120V socket may be designed to operate one appliance for a while, but a single appliance may be a very different sort of load than hundreds of watts of crappy LED.

Also, this whole idea of connecting an EV via a manual transfer switch involves running an entirely separate cable connected to an entirely separate point near your main panel. The cost-effective (but currently mostly impractical solution) is to use the same physical wires for charging and for islanded V2H.