Sorry for reviving an old thread, but there is a way to make those decorative custom content L-shaped stairs work (City Living Required to make them functional):
1) Find a decorative L-shaped staircase piece and place it in your home
2) Download this mod (Requires City Living): http://modthesims.info/d/611299/teleporter-and-elevators-for-community-and-residential-lots.html
3) Place Master Elevator Marker at base of stairs
4) Place Slave Elevator Maker at top of stairs
5) Enjoy. Unfortunately, due to how the mod was designed, your sim will just teleport to the top of the stairs whenever you route the sim upstairs. So no stair climbing animation.