Well this proposed solution is worthy of a sneaky Halloween trick, but ... it works ... kinda ... :)
1. put a real small label on your Form, set its Text to an empty string. set its background color to match the Form color, or you can even set its background color to Transparent. Or put it behind something :)
2. Define 'Enter and 'Leave events for your RichtTextBox1:
private void richTextBox1_Enter(object sender, EventArgs e)
{
label1.Focus();
}
private void richTextBox1_Leave(object sender, EventArgs e)
{
Cursor = Cursors.Default;
}