At some point over the next 12 months, I'd like to travel to Buenos Aires or Rio for an extended weekend (Th-Mo).
Nearly any weekend would do.

My only requirement is that the flights be direct - the reason is very simple.
I'm self-employed, and each day off is extremely expensive.

For a direct flight, I don't have to take off departure and arrival days.
I can fly out after work, and come back early am. In premium cabin, after a good night's sleep, I can go straight to work.
Layovers would make me miss work, and aren't worth it.

Miles - UR/UA 600K
BA - 300K
AmEx MR - 100K
AA - 100K
SPG - 100K.
Delta- minimal.

Checking with UA and AA, there isn't much availability in premium cabins, especially round trip. There is some availability in coach, and it's possible to upgrade cash ticket with miles.

Is it possible to book one-way saver, one-way cash with upgrade?
Is it less expensive to just book saver/standard award?
And finally, is there a way to set alerts in expertflyer or someplace else that would let me know award space is available?

Thanks!