You can create Triggered Emails for when an Account Payer needs to pay a Bill My Company Order. The email can be triggered to fire off of the Start Date or the End Date of the Event. For example, you can set up an Email Message to be fired 30 days before the Start Date.
This type of Triggered Email does not need to be assigned to a Product or Category -- it is a global Triggered Email. You can have multiple Triggered Emails of this type in your System. The email gets sent to the Account Payer just once, even if there are multiple Orders that need payment.
Login to the Administrative side of your database, and navigate to Settings --> Assignments --> Email Messages. Click to Add New Email. Input a Title, choose the type Triggered Account Payer Balance Due, and click the "Save" button.
You can now begin to compose your Email Message. Input a Subject, and add text to the Body. You can use plain text, and you can use Operators. Operators read data from the system that is relevant to the Account Payer and then input that data into the email. After you are finished composing your email message, click the "Save" button.
Creating the Triggered Email
Navigate to Settings --> Assignments --> Triggered Emails. Click the "Add New Triggered Email" button. 
Input a Title, choose the Type, select your Message, choose the date range that the Triggered Email will be used, and choose what will trigger the sending of the Email Message. If you want the Triggered Email to not expire, you can select No End Date.
The email gets sent based on the Event Start or End Dates. For example, you can send the email 7 days prior to the Event's Start Date.
