How to update Contact data with CDO data in Eloqua

Hi all,
I have a scenario where data is being imported from SFDC into a Custom Data Object (CDO) in Eloqua. My goal is to push this CDO data into a form submission. Since Eloqua doesn't support directly injecting CDO data into a form, I'm exploring how to first update the Contact record with the relevant CDO data and then use that to populate the form.

I'm looking for the best way to update Contact fields with values from the CDO (without using any 3rd-party apps). Has anyone implemented this approach or found a workaround?

Any insights or best practices would be appreciated!