Jordi, as far as I know there is no existing solution or plugin. This requires complicated custom code modification and it depends not only on the Oxwall functionality, but on the API they provide. You should create a kind of 'bridge' between Oxwall software and their functionality.

If you are not familiar with the plugin development, it would be better for you to find a developer who can help you with this plugin development. You can do it here: http://www.oxwall.org/market/specialists.