Using the KISS principle and assuming one can get a bit pf ply to fit the hive one is using, and strips of 8mm or 9mm thick, x 20mm pine make a rim round the board with a hole, say 4" long created by NOT putting in the strip.
Colony offering to swarm, cells with grub in seen.
Organise new brood box and have to hand plus board.
Find queen. Put her on her frame of brood in the new Briood Box and if wanted add another frame of stores and pollen, fill with foundation. Put on queen excluder and supers.
Put board on top with entrance facing away from the main hive entrance. IE North instead of south, east instead of west.
Put box with cells on top, removing all the most advanced ones. Check again in a week and again remove the most advanced ones.
Exercise patience.
Result will be a mated queen in the top box and a considerable amount of work by the parent colony.
And all vertical and no timetable as such to keep.
PH