By placing an open screened bottom board, a.k.a. an open mesh floor and a
screened top (a window screen splined into a standard window screen frame
available at any home store) in place of the usual inner cover, with the
outer cover propped up the ventilation will bring them in quickly.  I
experienced the same thing when I ran out of sbb's and had to use a
standard floor for a short time this summer.  When I switched the solid
floor out for a sbb, in they went.  In the Pacific Northwest we have
experienced the same temperatures as you have for most of July.
Additionally, you won't need a front screen to close them in, simply nail a
piece of wood across the front, the bees will have plenty of ventilation as
long as you keep them on a pallet or other boards to keep them directly off
the ground or trailer deck.

Replacing your inner cover for a mesh screen will greatly add ventilation
and allow the bees to dry out the nectar a lot faster, increasing honey
yields.  Common sense really, try to evaporate 10-20 gallons of water in a
small room with only a few small openings and you'll see how important it
is to maximize ventilation.

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