I've looked into it. There aren't really any good solutions for it besides a two system unit.
Adding another compressor to the system would likely force all the oil to the compressor that isn't operating, running the one that is dry and into ruin.
Then I came up with the idea of engineering a dual clutch/pulley system that would allow the compressor to be engine driven like it normally is, and then adding another pulley and clutch to be driven by a 120vac electric motor when stationary. This system might work well but I imagine it would be power hungry seeing the hp that road going ac systems require from an engine.
Then I started looking into btu requirements while stationary vs moving down the road and that there is a big difference between the two, and that one would likely be better off having 2 separate systems for travelling vs parked.