How to specify a gradient or other brush for the GroupBarItem background in WinForms GroupBar?

// Set up the Blend for the GradientBrush
Blend blend = new Blend();
blend.Factors = new float[] {0.0f, 0.0f, 1.0f};
blend.Positions = new float[] {0.0F, 0.5f, 1.0F};
// Estimate the GroupBarItem bounds
Rectangle rcgroupbaritem = new Rectangle(0, 0, this.groupBar1.Width, this.groupBar1.GroupBarItemHeight);
// Create and initialize the LinearGradientBrush
LinearGradientBrush lgbrush = new LinearGradientBrush(rcgroupbaritem, Color.White, Color.Red, 0, true);
lgbrush.Blend = blend;
// Assign the gradientbrush to the GroupBarItem1 of GroupBar1
this.groupBarItem1.BackgroundBrush = lgbrush;

' Set up the Blend for the GradientBrush
blend As Blend = New Blend()
blend.Factors = New Single() {0.0f, 0.0f, 1.0f}
blend.Positions = New Single() {0.0F, 0.5f, 1.0F}
' Estimate the GroupBarItem bounds
rcgroupbaritem As Rectangle = New Rectangle(0, 0, Me.groupBar1.Width, Me.groupBar1.GroupBarItemHeight)
' Create and initialize the LinearGradientBrush
lgbrush As LinearGradientBrush = New LinearGradientBrush(rcgroupbaritem, Color.White, Color.Red, 0, True)
lgbrush.Blend = blend
' Assign the gradientbrush to the GroupBarItem1 of GroupBar1
Me.groupBarItem1.BackgroundBrush = lgbrush