The first time I told them that I had dutied with in my household that prevented me from serving. Then they rescheduled me in the summer time. Bastards. I would just have your T write a letter stating that you are unable to serve. Worse case senerio, you go to jury selection and tell them you can not be objectionable. They will discharge you and send you home.
I dont think it will come to that though. I think a letter from your T will be enough. I wish you luck.