From OMA (or most midwest cities), look at flying on CO to the west coast (SEA/SFO/LAX) via FLL.

Book it using the multi-city option as:

OMA-FLL (early morning)
FLL-west coast city (late afternoon)
west coast city-FLL (redeye)
FLL-OMA (afternoon)

This will get 8500-10000 (depends on west coast city and which intermediate hubs are used) status miles (for NW or CO) for $250 or less over a single grueling weekend.

In general, the way to get extra miles on NW and CO domestic runs is to look at the valid routings for a fare and then book using the multi-city option strategically leaving out intermediate cities (usually hubs) that the will get filled in automatically.