Here's what I've been doing for the past couple years in 5/7, 7/8, etc. passages:
Find the smallest common multiple for the passage.
Draw notes on a blank piece of paper so that the RH set is above the LH set.
Draw little tickmarks indicating the miniscule subdivisions between each note.
Draw connecting lines between the two horizontal columns where the subdivisions match.
The point of this is not to be mathematically perfect, but rather to indiciate how quickly any given note in the the LH will fall before or after the nearest RH note.
Lastly, I go to my score, and draw in lines between the hands to show how the notes fall against each other. These lines give the general area of the placements, and not the precise math placement.
Even though this process may take half an hour to complete a page of Chopin polyrhythms,
for me it takes far less time and stress than to sit at the piano and just try to cram the notes together, which may be different every time.
Atleast this is how my brain works

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Eventually things will become more of an approximate collaboration between the hands rather than a regimented machine performance, which equals the danger that lies in this process.