How to generate BIP Reports with query on parent and child?

1) Navigate to Administration - BIP Publisher Reports screen

2) Select a Custom report template from the list and in the Integration Objects list specify the Search Specifications for the primary IC and a non primary IC.

For e.g. For an Account list report generated from the Accounts view we want to specify an IO searchspec on two fields at the Account (primary IC) and one field on the Activity (child IC).

We are looking for the correct syntax to achieve this.