You have to wait until mainland Europe. Pity, because there is a concessionary rate of VAT in the Azores.
I'm sure you know that deciding where to pay VAT in the EU is optional, and you must balance between the valuations being placed on yachts and local rate of VAT. You can't shop around though, where you declare is it. Portugal used to be considered good ... but my gen is a couple of years out of date.
My information is the reverse and that you can pay the VAT in the Azores if its your first point of entry. Unlike say Gibralter, Channel Islands, or the Canaries which are in the EEA but not the EU, the Azores is in the EU.
Although the Azores are in the EU, I am not sure that the Customs and Excise people there are set up to do VAT valuations and accept payments on imported boats. I think you would be better to delay registering until you reached mainland Europe. Either Spain or Portugal would be good places for first registration.
I am not, by any means, certain of the situation in ther Azores, nor are other people I have spoken to. If you are passing through the islands, it might be as well to call in at Ponta Delgada, the main harbour, to check the situation.