Green’s Dictionary of Slang

to do so, often as imper.

1932		‘P.P.’ Rhy. Sl. 7: ‘Come on boys “rats and mice.”’ [...] ‘All right, “Robinson Crusoe”.’.
1960		J. Franklyn Dict. of Rhy. Sl. 115/1: Robinson Crusoe Do so. The term seems to be derived from a late 19C. pantomime song: Mr. Robinson Crusoe – / You dirty old man to do so.