Your mentor thinks a shook swarm to be a bit drastic.
Shaking the complete colony, making sure to put a queen excluder underneath the new box of foundation for a week while they get themselves established so that they don't abscond.
Feed them well with 1:1 syrup and patty. There is no brood to feed, so the whole workforce is available to draw fresh wax, which if you keep up the feeding will be done in relatively short order - the colony will bounce back like an express train and be competing with the best of them in six to eight weeks time.
Patty - there are lots of recipes out there
brewers yeast powder (1)
soya flour (3) (just buy it don't dicker)
sugar (lots - think thick syrup)
Glug of cooking oil
egg yolk/s
Couple of large spoons of honey if you have it.
Hot water - to make the consistency of a pancake batter
Lemongrass oil, two drops
The lemongrass oil makes it sooooo delicious to the bees. Spoon it into fairy cake cups so that it doesn't run and use more cups rather than overfilling. the patty is good for beefing up bees for feeding duties as a pollen substitute.
Holland & Barratt can supply the brewers yeast powder £5, the soya flour £1.50 and the lemongrass oil £5 (all prices approximate, but very close). The wife can make merrengue with the egg whites, just before she kills you for stealing the eggs.
Thank you Hivemaker for the original recipe and the lemongrass oil tip.
All you have to remember is that brewers yeast is good for elements but is strong, so there is about three times as much soya flour in the mix. Sugar as another method of providing energy and honey to make it attractive, although as I have said the lemongrass oil is the main attractant. You don't need to be too prescriptive with the recipe. I fed 1 litre of the stuff to my eleven colonies at the weekend, their second portion and had previously used greaseproof paper instead of baking cups. Not a sign of paper or patty remained after a week, except in the weakest of the colonies which still had both some patty and paper left.
You don't have to believe me, just keep guessing and wondering if it might have worked for you. If in doubt PM Chris B and ask his advice re shook swarms and how they bounce back, in his experience.
Last year I shook one of my colonies as I had advised and co-incidentally it was the one that provided most of my honey crop from the supers. The second colony was significantly behind and the others had all been split to nucs for expansion and swarm control.
It was pulling in honey great guns but decided it was time to swarm in the first week of July, so don't think that you have necessarily stopped them swarming - they are Carniolans after all.