The mockserver allows you to define your mock data as javascript file and function that allow you to influence the behavior of the standard function to match your needs.
In order to define your mockdata, you need to create a file with the name of the entity set you want to mock and the extension .js in the folder identified by your mockdataPath.
You can then implement some functions defined in the API to add your custom logic.
Unbound actions are by definition specific to your application so the mockserver can't do much to help you there beside allowing you to implement whatever logic you need.
In order to define your own unbound actions you can create an EntityContainer.js file that will implement the function defined in the API.
By doing this you can add your custom logic for your unbound actions and mock what you need.