Japan is pretty sticky about admission (visas were required until recently), and most countries require showing proof of onward travel and only accept a ticket number -- not just reservations. So it really is necessary to issue the tickets prior to travel commencing. The e-ticket route is the obvious solution, and can always be arranged, as Gardyloo described. I think the alternative accepted by Japan is a letter of credit from your bank for some huge amount (USD 50,000) -- then they don't worry that you'll be a financial burden to Japan.