Temperature swings on bean growth

I'm having a hard time this season with alternating hot days and cold nights, making my beans growing far slower than what I had anticipated.

I planted the first 6 seed in tall pots about two weeks ago, and because there was an unexpected "chill" in the area the beans germinated late. Then, hot days followed, and the beans seem to be a little shocked by it and the growth has slowed down considerably; I should have at least a second set of leaves, but they are still on their first pair.

I can't keep the soil at a regular temperature because I am forced to use pots and containers to plant the beans. I don't have a patch of land I can claim as my growing area, so I had to use the roof, but because of the insulation it gets hot in the day and cold in the night.

There has to be a way around growing beans in pots on the roof, and I'm determined to find out if there's a way to keep the pot's soil at a constant temperature or build small individual greenhouses for the plants until they are established.

More on this as it develops.