I have an upcoming flight with one domestic segment connecting to one international segment.

I'd like to use miles/cash to upgrade to first class for the international segment (don't are about domestic upgrade that much). However, because it is one itinerary, Continental only offers the option to do it as if it were a single flight.

The upgrade is listed as 'waitlist only'. So, I can plunk down a few hundred $$$ and a few thousand miles to be on a waitlist.

Looking at the seat map, there are tons of empty first class seats on the domestic flight but only 2 empty first class seats on the international flight.

I'm platinum, so even if I don't try to put down cash/miles for an upgrade, I'll probably get upgraded to first on the domestic flight anyway (not that I really care about that one).

But, what happens if I lay out the miles/cash for the waitlist but then no upgrade is available on the international flight (but one is on the domestic flight)? Will I in effect will have paid for a very expensive domestic upgrade which I would have likely gotten for free anyway? Or, does Continental treat waitlist paid upgrades on such an itinerary as an all-or-nothing matter?

And, given that 2 seats are still showing as open on the international flight (which is 1 week from today), why is only a 'waitlist' upgrade available rather than just letting me buy one?