How much is it hitting the chain stay If its a minimal amount use the spacers that come with the GXP BB, At the LBS a fuji track pro had this problem, He machined his own GXP Drive side cup, With extended threads, and ran it with 4 spacers on the right, and i think 3 on the left (right being drive side- left being non) But the problem was the cups didnt last long, because the alloy he used was weak and cheap. But, he did clear his chainstay, I could ask him if he can machine them again. I saw his MTB at the store, That means. He'll be back O_O