Auto Add Fields to Custom Report Types (Beta)
How: From Setup, in the Quick Find box, enter Reports and Dashboards Settings, and then select Reports and Dashboards Settings. Select Auto add new custom fields to custom report type layouts and then click Save.
You can now add new custom fields to a report built from an existing custom report type from the Fields pane in the report builder. All custom fields for the Salesforce object are automatically included in the Fields list, and you can drag any of them to the Columns list.