To quote A Tribe Called Quest, "before I had status and before I had pager..." I requested an upgrade from C to F on a LAX-SYD flight, and got it.
It helped that it was a refundable fare...in fact, it was that legendary mistake fare, the r/t LAX-New Zealand for $1300.
Funny, that trip got me status on UA...and I haven't gotten an upgrade since!