Here are Luther’s own words from a Protestant site. It rather clearly shows that he rejects James primarily because James plainly refutes Luther’s new doctrine of Sola Fide.
Interestingly, the commentary shows the rather ambivalent feelings of many evangelicals toward the Bible; the commentator remarks on the fact that it was not the center of Christian belief before the Reformation, but also shows a rather nervous feeling about many books which have passages that don’t go well with Protestant ideas.
You might also mention Luther’s intense devotion to Mary:
It is a sweet and pious belief that the infusion of Mary’s soul was effected without original sin; so that in the very infusion of her soul she was also purified from original sin and adorned with God’s gifts, receiving a pure soul infused by God; thus from the first moment she began to live she was free from all sin" (Sermon: “On the Day of the Conception of the Mother of God,” 1527).