Create custom pixel block size in ArcGIS 10?

Question

I'm using the new IRawBlocks in ArcGIS 10 from the adopted sample in ArcGIS 10 SDK help and I want to create a custom sized pixel block that feeds me a block of values column by column instead of a block. So basically I'll be looping through each column in the raster. Any ideas as I couldn't find anything in the documentation?

        IRawBlocks rwBlocks = (IRawBlocks)rb;
        IRasterInfo rsInfo = rwBlocks.RasterInfo;
        IPixelBlock pb = rwBlocks.CreatePixelBlock();

        // change pixel blocks size here?????


        // iterate through pixel blocks
        for (int pbXcursor = 0; pbXcursor < rsProps.Width; pbXcursor++)
        {
            string line = "";
            rwBlocks.ReadBlock(pbXcursor, 0, 0, pb);

            // iterate through cells in pixel block, should only be one pixel column
            for (int pbHeight = 0; pbHeight < pb.Height; pbHeight++)
            {
                object val = pb.GetVal(0, 0, pbHeight);//pbWidth, pbHeight);
                // etc
            }
        }

Thanks Rob