The server does almost every hour check the repos, if there is something to push. Telling the DevZone to push your project to an other location is quite easy.
On Bitbucket.org, just give the user devzone write access to the repo you created there, if you have another server, you need to allow ssh with key, the public key of the DevZone.
Then you have an url which will be added to the push of the server. Create a file called "backup.push" and add it to the root of your repository.
Example of OpenGFX: http://dev.openttdcoop.org/projects/opengfx/repository/entry/backup.push