How can I let the user in a simply GUI change the orientation of the contextual menu?

Question

Have a checkbox. I'm trying to figure out how to let this checkbox change the default left to right of the special contextual menu I built. As the users have dual screen, and each person uses a different monitor, the contextual menu often gets split onto the next screen. I'd like to let them choose the direction, thereby keeping it on the same screen, but don't know how to allow the checkbox to change this default value.

Tips?

  private void menuLeftToRight_CheckedChanged(object sender, EventArgs e)
  {
       if (menuLeftToRight.Checked = true)
       {draftsContextMenu.??? = true;}  //need to change menu orientation
  }