Moving Earth before the Sun strikes

In around 4 - 5 billion years time the Sun will expand and engulf the Earth. How do we survive?

NewScientist has an interesting article entitled Moving the Earth: a planetary survival guide. They propose two possible methods to move the Earth away from the Sun's expanded surface: gradual nudges to the Earth's orbit through flybys of icy Kuiper belt objects or with a giant solar sail.

For some background and references on the future of life on Earth read my essay 4 billion years AD (pdf).