@DannyPancratz Thanks for posting to PX Community.
This is not currently possible using the PX Salesforce Integration.
While you could add a new custom PX User attribute to store this data, there is no way to automatically populate the field with the last NPS score.
Both of these would be a good enhancement requests to post our PX Community Ideas section for others to review, comment, and upvote, plus for our Product Team to consider adding to a future release.
Our other customers rely on their PX+CS Product Experience integration, the PX AWS S3 and Google Cloud Export integration, and/or PX Webhooks to bring this type of Survey response data into Salesforce and/or other business systems.
Happy PX-ing!