I have been supersonic a couple of times in a/c that had the airframe capability but not the thrust (no re-heat). I takes a lot of oomph to get throught the barrier. In both of the types the technique was to climb to fl450 then with full power roll inverted, pull the nose to 45 degrees down then roll right way up again. You were supersonic just long enough to say "wow hasn't it gone quiet and smooth" before pulling like hell to avoid making a bid hole and a nasty mess. G capability is much reduced when supersonic due reduced lift. Bearing this in mind I think the chances of getting a 747 supersonic and surviving it are pretty slim.