Once the bees have decided to swarm the best solution is to split the hive taking the queen away from the original location (even if it's only a few feet away) and letting the queen cells hatch a new queen.
You can either then recombine the two or build up 2 hives, which is the better. 2 hives gives you resources or saving 1 or both hives that you don't have with only one hive.
I have a package that is just about to fill the second 8 frame medium - full of brood in all stages, and I am thinking about provoking them to build swarm cells by continuing to feed and not giving them any more room at that point - and then moving the old queen to a nuc to head off the swarm.
How risky would this be? How often would I need to inspect to be sure and find the swarm cells in time to move the queen? Should I wait until they fill another box - or two? If I do wait then the inspections will get longer and more invasive as the colony gets bigger.
The idea is that swarm cells will make the best queen.
I would really like to have 2 hives going before winter. So far our weather is pretty stellar - plenty of rain and plenty of sunshine. Flowers everywhere. If the rain fails (it often does) I'm willing to feed from now till fall if I have to - our first freeze is usually after Halloween.