Fastest way to convert T[,] to T[][]?

So it turns out all arrays are not created equal. Multi-dimensional arrays can have non-zero lower bounds. See for example Excel PIA's Range.Value property object[,] rectData = myRange.Value;

I need to convert these data into a jagged array. My first try below smells of complexity. Any suggestions to optimize it? It needs to handle the general case where lower bounds may not be zero.

I have this ex method:

    public static T[][] AsJagged<T>( this T[,] rect )
    {
        int row1 = rect.GetLowerBound(0);
        int rowN = rect.GetUpperBound(0);
        int col1 = rect.GetLowerBound(1);
        int colN = rect.GetUpperBound(1);

        int height = rowN - row1 + 1;
        int width = colN - col1 + 1;
        T[][] jagged = new T[height][];

        int k = 0;
        int l;
        for ( int i = row1; i < row1 + height; i++ )
        {
            l = 0;
            T[] temp = new T[width];
            for ( int j = col1; j < col1 + width; j++ )
                temp[l++] = rect[i, j];
            jagged[k++] = temp;
        }

        return jagged;
    }

Used like this:

    public void Foo()
    {
        int[,] iRect1 = { { 1, 1, 1, 1 }, { 1, 1, 1, 1 }, { 1, 1, 1, 1 }, { 1, 1, 1, 1 }, { 1, 1, 1, 1 }, { 1, 1, 1, 1 }, { 1, 1, 1, 1 }, { 1, 1, 1, 1 } };
        int[][] iJagged1 = iRect1.AsJagged();

        int[] lengths = { 3, 5 };
        int[] lowerBounds = { 7, 8 };
        int[,] iRect2 = (int[,])Array.CreateInstance(typeof(int), lengths, lowerBounds);
        int[][] iJagged2 = iRect2.AsJagged();

    }

Curious if Buffer.BlockCopy() would work or be faster?

Edit: AsJagged needs to handle reference types.

Edit: Found bug in AsJagged(). Added int l; and added col1 + width to inner loop.