There is an additional component “Vector Drawing Tools” that allows you to create your own shapes and lines and use them along with predefined shapes. In fact this is a vector drawing editor inside Diagrammix! This component available as in-app purchase both for Mac App Store and non App Store version of the app. See menu Store inside the app.
Diagrammix
Diagrammix is the most efficient tool on the market for building attractive diagrams and charts