"I can't think of an example where any airline ever paid an overtime bonus (125 or 150%) for work voluntarily picked up"
Spirit pays 150% for picking up open time on days off. if they junior man, you get 200%.(On top of line guarantee)
DTW-(LAS,LAX,SFO)-DTW on a day off =18 hrs pay.(you levae at night, get home in morning two days later-basically one day away from home). If junior manned, 24 hours pay!!!