Hi Hans ,

Thanks for your post.

I am not familiar with Office automation. Normally, ContextMenu.Show()
method internally invokes TrackPopupMenuEx win32 API to do the actual work.
So we may do something like this:

[StructLayout(LayoutKind.Sequential)]
    public class TPMPARAMS
{
    public int cbSize;
    public int rcExclude_left;
    public int rcExclude_top;
    public int rcExclude_right;
    public int rcExclude_bottom;
}

[DllImport("user32.dll", CharSet=CharSet.Auto, ExactSpelling=true)]
public static extern bool TrackPopupMenuEx(IntPtr hmenu, int fuFlags, int
x, int y, IntPtr hwnd, TPMPARAMS tpm);

private void button1_Click(object sender, System.EventArgs e)
{
    Point pt=this.PointToScreen(this.textBox1.Location);
    TrackPopupMenuEx(this.contextMenu1.Handle, 0x42,
        pt.X+10, pt.Y+10, this.textBox1.Handle, null);
}

You can substitute the "this.textBox1.Handle" with your activeX window
handle value. However, I am not sure if this work for Office Addin.

Hope this helps!

Best regards,
Jeffrey Tan
Microsoft Online Partner Support