Create your own Office 365 workflow using visual studio and attach the workflow to lists on the host network

I am using Office 365. I need to create my own workflow using Visual Studio 2012. The workflow needs to be triggered when any item in the list in the web host changes, not in the web application.

The SharePoint 2013 project app allows you to create a Visual Studio 2012 Workflow project, but there is no way to connect to an existing list on your Office 365 site.