Javascript array: Negative Indexes?

It's possible to create a non zero based Array, using something like this:

var lengths:int[] = new int[1];

var lowerBounds:int[] = new int[1];

lowerBounds[0] = -1;

lengths[0] = 3;

var array:System.Array = System.Array.CreateInstance(Vector3,lengths,lowerBounds);

var vector3Array:Vector3[] = new Array(array).ToBuiltin(Vector3);

Most of the array methods don't support negative indexes though, for example you wouldn't be able to use:

vector3Array[-1] = new Vector3(0.0f,0.0f,0.0f);

But you could use:

vector3Array.GetValue(-1);
vector3Array.SetValue(new Vector3(0.0f,0.0f,0.0f),-1);