How to show matching incident rows from two different join tables?

We're working on a project where we want to add contacts to an incident, but we can't use secondary contacts because we don't want to automatically send emails to them. (That's a separate issue that needs to be addressed.)

So, we've created a custom object to hold these secondary contacts. Basically, it's a join table to link contact ids and incident ids, just like inc2contact. Let's call the table OBO.

We want a report that shows all incidents related to a contact, whether they are the primary contact or a secondary contact that is associated via the OBO table. So, we'd be filtering by contact ID (or other contact fields).