Free will can be produced in a machine that has either a random number generator or behavior that appears quite random to the ordinary observer. Turing, 1951.
The Turing Argument
Andrew Hodges quotes Turing in a summary of Turing's position:
"[Incorporating a free will element in a machine] could be done either by 'something like a roulette wheel or a supply of radium'--that is, by the kind of random number generator that worked like the Rockex tape generator, off random noise--or else by machines 'whose behaviour appears quite random to anyone who does not know the details of their construction.'" (Hodges 441-442)
Hodges, Andrew. 1983. Alan Turing: The Enigma. Simon and Schuster.
Turing, A.M. 1951. "Can Digital Computers Think?" Aired on the BBC, May 15, 1951.