Do flight attendants do pinch-hitter training?
This is generally not standard practice. For one pilot training is particularly costly (even just in small planes) and would simply not be worth it to the airline, which is why there are two flight capable people in the cockpit to begin with. 

Historically speaking there is evidence to the fact that it would not alter the outcome of the scenario. The closest instance of this occurring was possibly Helios Airways Flight 522 which lost cabin pressure at altitude incapacitating the crew and most aboard. Flight attendant Andreas Prodromou who held a UK Commercial Pilot License (but was not trained on the B737) was able to remain conscious via a portable air pack and make his way to the cockpit and into the captains seat. However he was un-able to take positive (meaningful) control of the aircraft due to lack of experience investigators eventually concluded after the crash. 

There have been some successful talk down landings of substantially smaller aircraft.

FWIW, most modern airliners are sophisticated enough and have the controls concentrated enough that they can be flown single handedly in a manageable fashion.