If you really want to use your 500 mile certificates in this equation, you could do this:

Get the AA credit card for 30k miles and then use 125k miles to buy a J ticket (JFK-LAX on AA and LAX-PPT on Air Tahiti).

Then, purchase a R/T Y ticket JFK-LAX, get one more upgrade certificate (AA’s been known to pro-rate at the end of the year, so maybe fly 2,500 miles by then) and try to upgrade one way. Then also purchase a R/T J ticket on Air Tahiti LAX-PPT. Complicated, but could work!