Does the food box get processed before the production box? I think it does. If so, you could do the following:
1) On prior turn, position engineer on forest, swamp, jungle, or mountain square adjacent to main railnet. If the chosen square is already on the main railnet, this can wait until next turn.
2) Build partisans in 50 cities on the same turn (obviously rushbuild where necessary).
3) Engineer from step 1 creates city
4) Partisans all ride rails/ship chains to newly founded size 1 city with empty food box
5) Rehome all partisans to that size 1 city creating a large sheild shortage.
6) Make worker in new city an elvis to create food shortage as city square will not support the citizen.
7) Voila! 50 none units when the city starves.