Upload an Attachment to a Customer Record (Not a Ticket)

We are migrating from another system and ran into a roadblock. We need to copy customer context notes and attachments from the old system to customer records in the new. We know how to use the API to add attachments to Zoho Desk tickets, but have been unable to see a means to add Attachments to Zoho Desk "Contacts."

Is the API capable of this, or can it be updated to include this function?