Cool that you've had some success at that, I'm glad it's worked out
Makes me wonder though...
Could you do a combination of these things? I wonder about starting the trapout, using your method iddee, with brood and getting bees into the appropriate new box; then after a week or two when they've started the queen cells take that box away and set another box in its place with the cone extended into it with a queen excluder over the entrance. Or like you said Jim, with the cone next to the entrance when she high tails it out of there. Then when she absconds the wall nest n the next week or two she's in the box. Then you end up with 2 hives from the trapout process.
I suppose it's just more work and may not work, just got me to thinking.