Audio problem: During the lion fight scene, George says "Here kitty, kitty, kitty" but his mouth does not move at all.
Audio problem: When George is in Ursula's apartment after his shower, Ursula covers his behind with a bowl, saying "Cover the booty." Her mouth doesn't move.
Answer: There's certainly no listing for him on the IMDb, which is generally good with uncredited appearances. Farrell was still working in the UK and Ireland at the time of the film, which was entirely US shot, and didn't become involved in Hollywood productions until about the year 2000, three years after GOTJ came out, which would seem to make it extremely unlikely that he appeared in it.