If the RT was less than the one-way, the "secret" (not that I'd call it that) was to throw away the return leg. Frowned upon by some airlines, but what can they do?

Since the RT costs $100 more, you have to decide whether it's worth it to buy a ticket with as distant a return date as you can get on the off-chance that you might actually need it or be able to change it to what you need for a reasonable fee.

A long, long time ago, I remember buying international tickets with open-ended return dates. Not sure if those are still available. I've certainly never seen them on Orbitz, but perhaps the airlines sell them directly.