If you're willing to spend a little more money for a lot more miles (and northwest miles to boot), you might want to consider just booking this as an open jaw round trip, such as LAS-FLL-SFO, for example. I didn't have a chance to do a ton of checking, but some poking around *might* yield you 5-7,000 miles for less than 250 dollars. (The best I saw on a quick glance was $341, which isn't great, but is certainly a better ratio than 500 miles for $129).

Steve