Advanced Guestbook 2.3.1 entry default to private

I want to let people only post private messages, so how do you make Advanced Guestbook 2.3.1 entries default to private? I can delete the checkbox, but how do you set its value to return to whatever makes that value private?

Open up templates/form.php and delete
<input type="checkbox" name="gb_private" value="1"> <font size="1" face="$VARS[font_face]">$LANG[FormPriv]</font>

open lib/add.class.php and find
$sql_usertable = ($this->private==1) ? $this->table['priv'] : $this->table['data'];

replace it with
$sql_usertable = ($this->private==1) ? $this->table['priv'] : $this->table['priv'];

and you're done. It's a hack fix but should do the job.