My travel agent in Indonesia in the past has created a booking for me. I think the booking expires within 48 hours if not paid, so in fact the 'booking' didn't exist when I used it, but it satisfies people asking for a piece of paper.

One other time I created a fully refundable Y class ticket. That was a bit expensive. I wouldn't recommend it. It's better to just get the cheapest outbound single and throw it away.

Or there are other ways with Photoshop or whatever.

Fundamentally, however, the 'return ticket' requirement is a bit silly.