Not quite a mileage run either, but....
Different airlines have fares of around $296 RT Vancouver--Miami. From Miami, American is $280 RT to San Juan. This brings the total to around $576, about $130 less than the CO fare. You can fly Northwest Vancouver to Miami to earn NW miles.
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Wait for another Southwest sale that brings Seattle--Ft. Lauderdale to $198 RT. Ft. Lauderdale to San Juan is $214 on TWA, and this fare should be around for a while. That will make the fare close to $410 plus tax-- domestic US tax only, no international tax. Plus the whole group can fly to/from Seattle and save the hotel night expense in Minneapolis. Not bad.
Just a thought......