How can I add a contact to internal address book (instead of Google Account) on Android 4.4?

I'm using Android 4.4.2 with my new Google Nexus 5. I have a question about adding new contacts. On my workstation I'm running my own cloud system. It is an Apache sever running eGroupware on it and I'm using Sogo-Connector and Synthesis Sync Clients to synchronize all my clients. I synchronize all my contacts and calendar data over my different clients such as Laptops and Mobile phones. Now I want also use the cloud to sync my Google Nexus. Adding a new contact on the workstation (or any other client except the Nexus 5) works fine and after synchronization the new contact is available on the Nexus 5. If I want to add a new contact on the Nexus 5 itself, I really want to force the Nexus to add it in the *internal phone addressbook* instead of the Google Account. However this option is not available, because the phone forces me to sync it with the google account. How can I add a new contact to the internal phone addressbook?