I have a conduit and I get the back-sweats pretty much no matter what.
I bet a layer or two of ridgerest pad aligned to rest on your rear hips/lower back to keep the majority off your mid/upper back would help some. Since the loads you typically carry in a conduit, in the summer are minimal, pushing it off your back probably won't add too much extra pressure to the top/front of your shoulders.
I don't think mesh will help unless there's space behind it with free-flowing air.
Curious to hear how this goes.