SQLCipher + PCL = impossible?

Hi, I want to use the Xamarin SQLCipher component to encrypt a SQLite database. Xamarin advises the developers to separate app projects into several sub-projects:

1. a PCL core project, that should contain general platform independent code
2. a project for a specific platform, e.g. iOS or android

I want to put the data layer (ORM code) and the data access layer into the core project, because these layers are platform independent. Therefore I'll need such annotations like PrimaryKey or Autoincrement. The problem is, that I can't add SQLCipher as an assembly reference here, because it depends on a specific platform, like iOS, so I can't compile the core project anymore.

Any ideas what to do or is my approach wrong?