I found a workaround for this problem, using Zapier. It does not involve any coding. 

1. Create a new Zap to transfer information from QBO to Google Sheets (or Excel, whatever you use) when Customer gets updated.

2. Create a new Customer Type (it doesn't matter what you call it) 

3. In the Customers section in QBO, you can mass-update all your customers. In the view section, make sure it shows 300 rows. That is the max that it will allow you to change at a time. Select all and update to the new customer type. 

4. This will update your customers and trigger Zapier into pulling the ID for you. 

5. If you have more than 300 customers, you will need to go to the next page and repeat the process until you have all of them. 

6. This will not get any inactive customers. You will need to re-activate them for this to work. 

Hope this helps someone!