Unfortunately, you'll have to override OnMouseDown on the ToolStrip to get the mouse down event for the grip. The toolstrip will only fire the Mouse* events itself if an item has not intercepted the event.
Here's a super-quick sample of creating a toplevel window when a ToolStrip's grip is clicked.
public class MyToolStrip : ToolStrip {
protected override void OnMouseDown(MouseEventArgs mea) {
if (this.GripRectangle.Contains(mea.Location)) {
Point ___location = PointToScreen(Point.Empty);
Form f = new Form();
f.StartPosition = FormStartPosition.Manual;
f.Location = ___location;
f.Text = this.Text;
f.FormBorderStyle = FormBorderStyle.FixedToolWindow;
f.ClientSize = this.Size;
f.Controls.Add(this);
f.Show();
}
else {
base.OnMouseDown(mea);
}
}
}