Is this so you can get a good letter of rec? If you can't take a seminar with them or tutor for their course as an above poster said, why don't you just state your intentions openly and ask for a letter. It is always best (in my experience) to ask for a letter once you have completed the course with that professor. If you want a professor who knows you very well to write, then maybe you should try to get letters from professors who have taught you more than one course, perhaps organic 1 and 2 or physics 1 and 2 if they're taught by the same person.
Also, being your résumé in for the professor to have a look at it. Perhaps there will be an experience you have which they're interested in. From my experience, most professors are involved in more than just teaching their course. They give seminars, do research, or mentor clubs. See what your professors do and latch on if you're interested. This would allow the professor to learn more about you this hopefully resulting in a better letter of recommendation.