I recently encountered the same issue, what you can do and what worked for me is to ask the seller to go to the Pakistani embassy (very tough to convince though) and submit a formal statement which clearly states that he is no longer the owner of the vehicle and terms you as the real owner. Its a long and unclear process but worked for me so with trial and persuasion you should be able to get it done.
get the copy of the statement and thereon you'll have to get a court order, get an agent to get it done for you.
Thereon youll have to take those documents to ETO office and should work out fine.
Very long and cumbersome process but thats how our local systems are designed, have to live with it.