I blagged it once. I was working with a Jazz monster pianist (and a drummer who would call out the changes to me when I got lost) who called a tune called Oleo. He counted it off at INSANE bpm in the rehearsal. I said that I could not think at that speed, let alone follow a chart. He told me to just play anything and he would cover me. I laughed. He said no, do it. On the gig he played the whole thing "outside" but with clearly discernible melody and solos while I played absolutely abstract walking lines which did not follow any discernible pattern at breakneck speed. I had NO idea what was going on but looked like a Don. Obviously I have blagged it many other times, but that was the best of them all. I still cannot work out what he did.