Elkhorn creek

The standard approach to Mt. Idaho is from the west via Elkhorn Creek. There is a small dry ravine on the north side of the canyon that gives you access to the west ridge of Idaho. I recall looking down from there into the canyon you're talking about (the one that is south of Borah and ends at Idaho's west ridge) and thinking it would be a long day but doable route. If there's snow on the slope leading up to the ridge you may have an easier time of it since you can avoid the scree.