Many/most international round-trip rules allow you to combine half of one round trip with the 'return' half of another round-trip. Thus pay half of the round-trip fare for the direction you want to fly, and (illegally) throw away a really cheap coach return.

"Most-restrictive" rules will apply to the pairing, e.g. if one half must be flown within 90 days and the other gives you a year, you'll only have 90 days (if the rate desk is paying attention).