I was late in planting my beans this year and whilst everyone else in the village was enjoying theirs, mine were still in pots. However, I am reaping the benefit now as the village people's beans have all finished and I have hundreds. Many still have flowers and the bees are loving them. I have been putting many of the beans on the village produce table where proceeds go to cancer research. They are selling very quickly. Next year I have decided to stagger my planting so I can have fresh beans for a longer period.
I have never grown any beans in the greenhouse though I always start mine off in there. I would be interested to know how you get on with yours as it could extend the growing period even more. The problems I see are that you would need to leave the door open during the day for the bees to get in and this would lower the temperature. It may be beneficial to put fleece over the beans at night when temperatures start dropping. Good luck!