Okay, got an answer from Blackberry itself, which said that it's not possible at the moment. If required, you can build your own cordova plugin by extending the original plugin at https://github.com/blackberry/cordova-blackberry-plugins/tree/master/plugin/com.blackberry.pim.contacts
They even provide a template for custom plugins at https://github.com/blackberry/WebWorks-Community-APIs/tree/master/BB10-Cordova/Template