Can you get a ticket without being paced, caught on some sort of radar, or a time trap....sure.
Would it take anything more then a semi retarded monkey to fight it in court and win...NO.
A police officer's eye ball is not a caliberated peice of machinery. Unless your speed caused an accident or almost caused an accident it's not "unsafe" in my eyes (and I'm sure the courts will agree). Unless you do something silly like pass a cop who is already going X amount of speed and he can say "I was going 40 in a 40 and the car past me at which appeared to be a high rate of speed" then it's not much that can be done.
Can a police officer issue the ticket...sure...people get arrested all the time who are found innocent. Same thing.