Hey OP,

Is it impossible to bump the flight back?
You could do the 15th-20th and bump those flights back a day.

What date and time are your flights back to Australia? You could also look at the direct flight from Easter Island to Lima... its once weekly I think. Unfortunately this can't be done if the Santiago - Lima leg is on the same airline as the Lima - Australia leg.

PS Your post gave me a dose of nostalgia. I was on Easter Island from May 12th to May 16th last year. Where has the time gone...??