Hi Ajay,
when you define your rapid application there is a step where you define the UI model.
There expand the UI element type Embeddable Search and select the Search Result view. In the second assignment block you will get a list of fields. there in the column Search Criteria check the field you want to map with i.e. opportunity id. then you will get the field while mapping.
Just remember before you update your rapid application, remove it from the overview page configuration, remove it from embedded views list and then update the rapid application.
Please refer the the link http://scn.sap.com/docs/DOC-5404. you will see although the membership type is not a key field, how the presenter checks the search criteria checkbox and so it is available for mapping in the 2nd part of the demo(the previous link i shared).
Regards,
Sayan