If there are multiple CDO records mapped to a contact, which CDO record would a signature rule use?

We are working on creating automating our contract renewal notices through Eloqua. Renewal opportunity data is synced from SFDC into a Custom Object table (CDO) based on the Opportunity Contact Role SFDC object. Renewal rep information is populated in the email based on the opportunity owner ID field values in the CDO. 

A contact can have multiple Opportunity Contact Role records, as a new renewal opportunity would be created for their account every year. With rep churn and territory changes, the renewal rep can change from year to year.

I have built a signature rule which references the Opportunity Contact Role CDO; however, it doesn't look like I can define which record within the CDO to use if there are multiple records against an email recipient.