It’s very easy. You just need to follow these steps:
1. Access ‘Your Contents‘ from your user area.
2. Click on the option "Publish".
3. Click on ‘Multi-channel‘ or scroll to get to that section and copy your promotion’s url.
4. Create a new external web application and paste the html link.
Then copy the promotion link you copied earlier (you can give a specific height to the new promotion page) and adjust the content thanks to our zoom:
5. Post the new tab you’ve just created on any Fan Page you want. Your contest will now be published in 2 different Facebook pages