This is an interesting topic.
I think the answer is to make Japan and Asia more valuable, in particular relative to Europe and Africa. Looking at a map such as WW2 Revised, where the USA tends to go very heavily in Europe. Why doesn't the USA go Pacific? You mean why doesn't the USA target Norway (worth 3), Algeria and Libya (worth 1 each), and then Western and Southern Europe (6 each) instead of 3 islands worth 0 each?
So I don't think the answer is to force Russian-Japanese neutrality. If Japan cannot affect the land war of Eastern Europe, it just makes going Pacific an even worse strategy for the USA.