No, but the following code will do it for you:

void DropDown_Layout(object sender, LayoutEventArgs e)
{
    StripSeparators(((ToolStrip)sender).Items);
}

public void StripSeparators(ToolStripItemCollection tsItems)
{
// ItemCollections should neither begin with, end with or contain adjacent separators.
    bool itemDisplayed = false;
    ToolStripItem lastSeparator = null;

    foreach (ToolStripItem tsItem in tsItems)
    {
      if (tsItem.Available)
      {
        if (tsItem is ToolStripSeparator)
        {
           // hide all separators
           tsItem.Visible = false;
           // only set in a separator that has a chance to be shown later
           // if no items have been displayed, no chance
           if (itemDisplayed) lastSeparator = tsItem;
        }
        else if (lastSeparator != null)
        {
           // show it when valid
           lastSeparator.Visible = true;
        }
        else
        {
           itemDisplayed = true;
        }
      }
    }
}