I treated every rotation as if I were seriously considering going into that field of medicine after my training. You might get more out of each rotation if you approach it this way. Even Ob/Gyn I approached w/ a bias, during it I was surprised how fascinating it all was and for a minute even considered it as a career.
Although, I'd had my heart set on Urology, my critical care elective changed all that. Like I said, have an open mind, you'll get more out of your rotations this way. If not, then just lie to your preceptor :)