Selling a car I just bought - haven't received V5

Hey guys, I just bought a used car a few days ago. The seller has sent off the V5 and given me the green slip and I am currently waiting for the form to come in the mail. The problem I have is that I have to move back to Australia at extremely short notice (in the next two weeks), and need to sell the car on, which gives me almost 100% not enough time to not only get the confirmation in the mail, but also send it back and then wait longer for the new logbook to get to me (I heard up to 6 weeks).

What are my options (if any) in selling he car in the next two weeks, assuming that I almost certainly will not get the new logbook in time? If I get the confirmation in time, can I not send it in straight away, sell the car, and get the new buyer to send it in? Any other ideas?

Thanks!