If your bike computer can transmit to the rear wheel, you should be able to easily do that without going to the LBS. If you are in the market for a rear-wheel sensor system, I recommend the Cateye. It is small, wireless, and measures cadence as well as speed with one sensor and two magnets. I have requested a spare magnet for x-mas so I don't have to change it out every time I change the wheel for the trainer.
I stand and rejoice every time I see a woman ride by on a wheel...the picture of free, untrammelled womanhood--Susan B. Anthony