How to add content to an extra column in grid using ATK

How to add content to an extra column in grid using ATK

I have a grid that gets its content from the QuestionCollection model.
In one column I want to show the questions in the collection. I use three
models to connect questions to collections:
Question
QuestionInCollection
QuestionCollection
That is, I want to show content connected to specific rows in an extra
column, which is added to the grid with addColumn. But how do I insert
this content to each row?
I have tried using setTemplate and addSource, as well as extending the
QuestionCollection model with an extra 'question' field. But I cannot get
it to work. Any ideas?