Sorry, but that exactly what the Devs want to prevent happening. This is pretty evident when reading 1.1.2 patch notes and seeing how they handled Nemesis spawns for high level characters in low level areas.
For farming leveling uniques, If you already have a high level character, you’d be better of just running the highest level content you build can handle. This will also grant you leveling uniques, just with better odds of having higher LP.