Just wanted to post a quick update for anyone else who might search for this in the future - after a million e-mails and a couple of phone calls to Spain I have learned that if you're an EU National (even if you're not living within the EU at the moment) you DO NOT need to include a pre-paid envelope with your application. Supposedly they will process the certificate once they receive all of the documentation (Form 790 + apostolised passport copy (which you can ONLY get at the Spanish Embassy in Wellington if you're in NZ already) + proof of payment) I am sending out today and will send the certificate back to me via e-mail and through post to New Zealand (at their expense). I'll post another update here once I (fingers crossed) receive the police clearance certificate.