I did it at TPA last year. NW had no problem doing from my DL ticket. The only problem was no FC available to DTW, but FC was available DTW-GRR. I still didn't mind, since I would not have been in FC on DL anyway.
It is my understanding that they wound do the bump on international flights. Anyone have actual experience with this?

BTW, I would only do this on your return. A co-worker of mine tried this on the outbound and found his return was cancelled by the original airline. He got it worked out, but it was a major pain.