You can't.
KLAX use the default jetway system, which doesn't support more than one jetway. When we'll upgrade the scenery to use SODE, it can support up to 4 jetways on a single stand.
And, on a scenery that use the default jetway animation system, the first jetway (the one and only one that FSX can use), will go to the door flagged as the main exit in the [Exits] section of the airplane, so it's entirely unrelated to the scenery, which has no control over it. This will also be fixed with SODE, which allows to dock any jetway to any door, provided it can be physically reached, of course
