AS plans for the Michael Jackson concerts were blown to smithereens last week, word filtered through of ''Wacko's'' characteristically eclectic plans to mark his arrival in the territory. Jackson planned to fly in under conditions of enormous secrecy several days before the first concert was due to be held at Sha Tin racecourse on August 15. The reason for his undercover arrival was because two or three days before the gig, Jackson was to have boarded a traditional Chinese sailing junk and navigated his way through Victoria Harbour sitting on a throne on deck dressed like an emperor of the Middle Kingdom. The vessel was to have sailed into the basin of HMS Tamar, where Jackson was to have alighted and then been ferried by a waiting rickshaw to a private gathering of children from 10 nations dressed in ethnic costume who were to have presented him with cheques made out to his favourite charity. With the British base a restricted area, the site could have been protected from the close attentions of the media and his fans. But the cancellation of the concerts has also forced this event to be dropped, with the Jackson camp forfeiting the money they had paid to use the British Forces headquarters.