I could be wrong but I wasn't aware that you can actually register the car at the embassy. My understanding, although I have not done it myself, is that you can get all the paperwork you need validated by the embassy so that, when you come to register the car in Crete, you pay a relatively small fee rather than the extortionate fee that they usually charge. That's always assuming that the authorities in Crete accept the paperwork from the embassy. No guarantees there I am afraid. I know of people who have done it but I believe, having sorted out all the paperwork themselves with the embassy, which took several trips, they still paid an agent in Crete and it cost around 2,000 Euro.
PS It sounds like quite a big vehicle? Is the engine under 2 litre? If not you will allocated an assumed income in Greece based on the engine size and taxed on that income even if you earn nothing. You can avoid this tax only if you bring into Greece more than the assumed income every year and get validation documents, usually referred to as pink slips, from the bank.