Sometimes things really are easy – the fact that I Googled how to do this now seems pretty silly. The more I use JSF the more I like it 
To initialize the state of the ManagedBean that a JSF page is using (like to preload data, or initialize other displayed values), just call the code from the bean’s constructor. Simple as that.
For example
@ManagedBean
public class ExampleController
{
private String exampleProperty1;
private String exampleProperty2;
public ExampleController()
{
//example init code here, e.g. to init property values
}
...
}