Adding list collector as breakdown source

I have a requirement to be create a report on incidents with a custom list collector as a breakdown.

Looking at this post I tried following a reply by @Adam Stout that says you should be able to use PA breakdowns on lists, but I don't really see how.

When creating a new Breakdown source I cannot add my list collector as the 'Field' for the breakdown source, it is greyed out when I try to add it. This makes me wonder if it is at all possible.

Best regards,

Kim