It does not appear that a city's population decreases when demolishing housing.  Then new housing just adds to the total, so the maximum population is higher than it should be.  For example, I had two kingom huts (for a total population of 35).  I then deleted one, and built a new one.  Even though I still only had two kingdom huts, I now had a maximum population of 45, and the city leveled up a few turns later (upon reaching 40 population).

I have not played around with this much more than just confirming that it is happening, but I would guess that repeatedly building and demolishing houses right now would allow as much population as you desired, without using more than one  subplot.