IN few words... Impossible.
We asked Mr. Fabien Potencier something like... "Will be possible to migrate from symfony1 to symfony2?". His answer was much short than mine... NO.
Symfony2 has nothing to do with Symfony1. Only share name, no more.
Start new project in SF2, try to understand how it works and you will be able to mantain project with new features.
Migrate is bad...