Working with a Data Layer / Send Data from Website to Eloqua

We are working with Merkle, who is placing a JavaScript snippet on our website that will retrieve a customer's email address from their database and add it to the browser's Data Layer. The goal is to send an email to the user.

From my research, we can utilize Eloqua's Web Data Lookup (WDL) to take the email address from the Data Layer via the Merkle JavaScript and check if we have that user as a contact in Eloqua. Since WDL is a read-only solution, I need to find a way to get the user into the Eloqua system (Segment / CDO / List) so they can be included in a campaign.