Book your outbound at 330 days, with UA. They WILL hold that reservation for 14 days. At 14 days you call back and make your inbound reservation (ya, I know you're not coming back in 14 days). With UA there is NO fee to change the date or time of your flight on award travel. The only time yoy pay a fee is if you change city pairs. So, when you get to 330 days out from your REAL return flt. you call and change the date. Simple. I've done it. No fees.

BTW, UA now charges a small fee if you CALL and make your award reservations. Fee is waived if you book online. Not a good idea in your case.

Phil