Seeking guidance on how to store data from one input element into separate metadata

[Elle H]

The selected value (Last Name, First Name) from the Author input element on the item form is stored in dc.contributor.author. I want to store the Solr ID of the selected value in a separate metadata field. I read the custom configuration documentation and tried it. I ended up with a new input element which I’ll call Author ID that behaved the same as the author onebox; this was redundant and horrible from a usability perspective . Is there a cleaner way I can simultaneously store the author name and Solr ID after searching for and picking authors from the Author onebox?