How best to isolate dirty power caused air conditioners or other motor driven devices at the dirty device itself?
Well after plenty of research the proper device is a online sinewave UPS that is sized to handle the startup load of the motor/compressor. See https://www.apc.com/us/en/faqs/FA158851/ This answers the question above as posed; however, said UPS is prohibitively expensive.
As for my flicker issue (the symptom) I solved it by wiring in inexpensive EMI filters into the affected fixtures.