There's probably a way to do this with a living sim but I did this by having a ghost in my household as you can continue to play with them and give them new aspirations. You'll also not be limited by the length of life as they're already dead.
I also tried to choose the aspirations that were based mostly on skill building. Some aspirations require the sim to reach a certain level in a career, so I avoided these as I felt these would be too time consuming. (You can check each stage of an aspiration before selecting it if you're not sure)