Metchosin, "Jury rig" was originally from INjury rig and was a temporary repair to a piece of shipboard equipment for either safety or to get the ship into a position to make,or have proper repairs.
As to "Bo-jang" I have heard the term to "Banjo" somethiing so maybe its a slightly "spoonered" version of this.
I have personally seen the ad in West London that says" you've tried the cowboys now try the Indians"