Polygon Gradient Fill in Immediate mode?

Is it possible to add a gradient fill to a polygon while using Immediate mode?

There isn't a parameter for it just Color.  Setting the Draw.GradientFill beforehand does nothing.

For example: 

//coordinates are in the 0-1 range, gradient should go from cyan to black.

using( Draw.Command( cam ) )
{
    Draw.GradientFillType = FillType.LinearGradient;
    var gf = new GradientFill();
    gf.colorStart = Color.cyan;
    gf.colorEnd = Color.black;
    gf.linearStart = new Vector3(0, 1, 0);
    gf.linearEnd = new Vector3(0, 0, 0);
    Draw.GradientFill = gf;
    Draw.Polygon(pgpath);
}