I heard this phrase at the Comedy Store in London when an old man was performing at the gong show. I can only presume that the heckle "Do a Morecambe" meant to have a heart attack whilst performing, as did the much-loved British comedian Eric Morecambe, who many would consider to be one of the greatest comedians of all time. (Although technically Mr Morecambe had his heart attack in the wings after the show.)
Old stand-up: "..."
Heckler: "Do a Morecambe!"