The freeways are superchargered well enough, although Mountain Home would sure help for when you're driving into a headwind in the winter.
There's a hole though from Ontario, Oregon to Coeur d'Alene along US95 and another along US93 through Salmon, as you indicated. The former has a CHAdeMO in Lewiston, Idaho and Pullman, Washington, which help. South on US95 isn't great either, but again there's a CHAdeMO in McDermitt on the way to Winnemucca.
In both cases you can go around, at some cost in time. Along I84 around through Kennewick to avoid US95, and on I15 as you noted through Lima, Montana the other way. Since you're starting in the middle, you might make it to Missoula from Hailey if you've got good range and under good conditions. Especially once this new plug in Hamilton, MT finishes.
Check plugshare for chargers, and it can definitely be helpful to invest in a CHAdeMO adapter out here to help you out of tight spots in rural areas.