Create a reference set relation form jobtype to job options. ( In the reference selector on jobtype add a new button to the control bar of the reference selector if you want to create new options from within the jobtype. If not wanted leave out the new button and add the joboptions to the menubar to add these separately from the jobtype. On the job options create a boolean attribute to set the option as default. Then add an event to the jobtype entity that retrieves the joboptions with the boolean set to true and creates the reference to the jobtype. You can do this on after create for example.
I hope this helps