The IngewikkeldWrapperBundle adds a fallback route: Any URL not caught by your Symfony2 code will be forwarded to your old symfony 1 project. This allows for gradual migration to Symfony2. For an explanation of the thought behind all this, please check this post on the Leaseweb Labs blog, where I've guest-posted about this way of migrating from symfony 1 to Symfony 2.
The IngewikkeldWrapperBundle is currently in a proof of concept-phase, but works already for one of my sites. I welcome any feedback and contributions :)