If you want to solo it I know 1 way. Breed the move in to Rattata/Diglett/shuckle/nincada/zangoose/seviper, then put quickclaw on them, enter smeargle safari and battle it, then kill your lvl1 Rattata/Diglett/shuckle/nincada/zangoose/seviper, and let the wild smeargle sketch it, then let him use it on your smeargle as you use protect with your smeargle, this will make Final Gambit fail and wont kill the wild smeargle, and then sketch him
tl:dr You need to make Final Gambit fail in combat, then you can sketch it,