Why would you be worried about swarming now? How many frames are drawn, how many aren't? Keep the brood nest open by moving frames around first, then add more room when they've filled the first box up.
It all depends on your area. 80-90% means nothing to me if they can't cover them all or if the queen hasn't laid up all the area she can. If you want frames drawn out quickly, you let them get a little crowded even, then you can add a box, checkerboard them and they'll have them all drawn out and laid up in 3 weeks and ready for a third box. Of course this all depends if there's a flow or not, if you're in a heavy flow it's good to stay a little or even a lot ahead of them but moderate to slow flows it's best to wait til they actually really need the space before giving them any.
I am not familiar with your flow but I would wonder whether they will be inclined to draw out much more comb. I have some two and six frame fillers and also have frame feeders to fill space in a second box rather than putting a whole box of undrawn comb on this late. They generally draw comb better in cooler weather if they are a bit more toward crowded conditions. I have bees with a fair bit of Carni breeding and have had them swarm after a week of rain. The queen shuts down laying if nectar and pollen is not coming in and the bees think their queen is failing perhaps. Crowding is not the only cause of swarming.
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