There's more to it than that, but the end result is to have the unsubscribe links populated into the email template.

The caveat is we need to render the template PRIOR to sending it via email using the template renderer because we are adding custom data sources to pass into the template. In order to do this, our only option with suitescript is to use with N/email "send" or "sendBulk" as these options allow us to pass in the template "body" (already rendered). It appears the only way to get the unsubscribe links to appear is to use the "sendCampaignEvent" method, however that does not allow us to pass in a rendered "body" and only allows the campaign event ID which