OK.This could not have been the right approach, because, as most people would agree, the Bible says it's wrong.
That the Bible says it's 'wrong', if that is indeed what it says, isn't binding in a secular 21st century society.
They would have been tempting them to act against what their scripture teaches (ie apostatize) in order to keep their licences. The best thing would have been either to disqualify all church ministers from acting as registrars, as NS said, or allow them to do so without requiring them to conduct SSMs.
The former, Spud, aside from clerics who are prepared to act as registrars without discriminating.
The issues of marrying same sex couples and giving practicing homosexuals positions in ministry, both of which a church is currently not required to do, would involve a minister doing something that is against biblical teaching, and thus illogical.
I'd have thought the church could do with all the talent it could get. Given, however, that the Bible has been 'interpreted' to within an inch of its life I'd have thought there would be no problem in doing so again. If not, the adherence to 'scripture' seems like a do-it-yourself hangman's kit.
To disallow ministers of religion to act as registrars (for heterosexual couples) would likewise be illogical.
If they can't stop discriminating then they need to relinquish the role - marriage is an important institution so it is best kept out of the hands of homophobic bigots.
This is because the marriage service in (say) a Christian wedding is by nature more valid than a simple civil ceremony, since it is done in the sight of God and includes promises of lifelong faithfulness etc (which civil ceremonies do not require). It thus makes marriages stronger.
This sounds like special pleading Spud - have you asked those who married without a religious input if they feel less married than those who did the church thing?