I think a bigger problem is that your winter nights won't make lowlanders happy and rest of the year won't make intermediate/highlanders happy. My gut feel is that it is going to be harder to get lowlanders to survive very cold winters than it will be to get intermediates/highlanders to survive summers with an assist. That said, you could try both. People who live in colder places could explain what they do to keep their lowlanders alive through winter.
As someone who grows in very lowland conditions and manages to keep several intermediates and highlanders alive, I can confirm that at least in my conditions, a misting system does produce dramatic results. The key is to use it to create more of an ambient humidity than watering of plants or even wetting of leaves. In peak summer, my misting can be set for 5 seconds every 5 minutes. Use as high pressure a system as you can afford, run it on a timer. The higher the pressure, the "drier" the mist - meaning, very small droplets are produced, which flash evaporate from the friction of being forced into the air. This works to create a temperature drop even in high humidity.
Aim to cool and humidify the AREA they are growing in, not the plant.
I am not going to pretend that all is rosy. Peak summers can be brutal. Many highlanders will not pitcher and will simply hang in there with somewhat slowed growth - my night temps in summer are consistently above 27C for several months. You may lose some plants. but overall, combined with watering with cool water... it is possible. One tip - automate everything needed to create stable conditions. The more stable the conditions you can give them - even if ****** and 15 degrees hotter than their preferred nights - the more the plants will adapt.
You should also research about species. Many intermediate/highland neps tolerate high temps better than others. Highland truncatas/veitchii, burbidgeae, anything from the maxima family.... too early to say but possibly lowii too. Another good hack is highland x lowland hybrids.
In my conditions, good ventilaion is MUST. I keep any use of plastic to retain humidity to an absolute minimum. Leverage evaporative cooling to the HILT. Big earthen pots or sphagnum in net pots, keep plants close to each other, water generously so that the whole area is soaked and dries off taking heat away. But don't use ice/very cold water.
One useful trick is to buy them just after the summer is over, so that they have time to establish and grow robustly before the next summer heat challenges them. Plants that are not well established are more likely to die.
