How to attach attachments via WF_MAIL.SEND

Currently, the customisations the business have made in the past utilise UTL_SMTP to send emails directly out of the database tier. This poses a problem to us as we have the email override setup at the apps tier, but the instances where we still use UTL_SMTP aren't affected by this; therefore causing emails to be sent out from test/development systems as we can't redirect these emails.

I have figured out using the workflow mailer via WF_MAIL.SEND and the 'oracle.apps.wf.notification.send' business event, which has worked fine. However, now that I'm starting to transition everything else to use this method, I can't figure out how to attach attachments to the mail.