Years ago the company I worked for had a fleet of Chieftains flying RPT. A requirement for single pilot RPT ops is that the aircraft be fitted with a serviceable autopilot. Every now and then the autopilot would become unserviceable, and the aircraft could be dispatched under the MEL. This required a second pilot, rated on type, with a command instrument rating, and holding a CPL or higher. The operation was somewhat "Micky mouse", with no formal training provided, other than a check ride, and left to the Captain's discretion as to how the ops were conducted. This included whether the "co-pilots" were to be given any actual flying, including Take-Offs and landings!
My understanding at the time was that these guys all logged co-pilot time as it was a "bonafide" op sanctioned by the regulator. Otherwise what would be the point? Just under what reg this was applied to, I must admit I haven't a clue, but I'm sure there'd be some single pilot ops out there somewhere that would have a similar proviso for U/S autopilots, or something equally applicable.