Okay, first, you need to make a sim with a load of cash. We're talking RICH. Also, two players.

Next, move the sim home, so he/she won't need to work. Next, build a completely new room, walls and all, and add the best of everything you need:

Beds, Refrigerators, Skill Builders, and above all, things that give you atmoshpere!

Get the atmosphere to a 10 rating, and move a new, poor sim into the building. He/she won't need to work, and can work on his/her skills in a great mood (the atmoshpere is needed to put your sim into a good mood).

Now, once you feel satisfied with his/her skills, you can get him any job he/she wants, and get promoted quickly.