The one I was originally thinking of has a gate, and is marked as Middle Kootenay Pass. That's not going to work. Looking at driving a little farther on the highway and trying out Ptolemy Pass which should take us to the Corbin Mine, and from there there are several options it seems. Need to do a bit more research. Thanks for the info guys!
The whole thing is kind of dependent upon the stars lining up just right anyway, we'll see if it actually happens.