Just look at the HTTP "Host" header and deny redirection requests when someone is using coinurl.com.
$_SERVER['HTTP_HOST'] gives the same result for "coinurl.com" and "cur.lv".
I have setup redirect using "Parked Domains" in the cPanel.
If the possibility of using coinurl.com instead of cur.lv was just a quirk, I would treat it as another way of bypassing the restriction and not wordfilter it.
As you can see on CoinURL main page, I never urge users to use coinurl.com domain for their links. You are right that using it is just bypassing of your restriction, as well as using goo.gl, bit.ly and whole bunch of other domains. I will be very grateful to you if you will remove the filter for "coinurl.com".
so someone might try using one of these links without seeing the warning on annoyance.php.
I never do this. If someone bypasses restrictions, just block him.