How can I add multiple transactions when calling render.mergeEmail with a template

I am creating a scheduled script that retrieves a list of unacknowledged Purchase Orders, then stores them according to the Vendor Id before emailing a list of transactions to the vendor. When storing a transaction, I store the internal ids of the vendor, transaction, and employee contact, so in the end there can be multiple transaction ids going to a single vendor. I have successfully merged these records with an email template, but only with a single transaction id. Is there a way to add x transactions when calling render.mergeEmail and reference each within an Email Template?

Here's my code that works for sending 1 transaction: