Vehicle transfer from outside Thailand

I purchased a Honda Wave a year ago, and now it's time to sell it. My problem is that I have temporarily left Thailand. I no longer have a rental contract or a valid residency certificate. I have someone willing to buy the bike, but I won't return to Thailand for 2 months, and even then will stay with friends instead of signing a rental agreement. 

Is there any way to transfer ownership to the new owner while I am out of the country? Can it be done without a residency certificate? Is there any paperwork I can sign as a workaround? I really appreciate the help.