Hello, jalterman. 

I understand how the workflow you're looking for is beneficial to your business. However, as of this moment, the ability to set up a credit card processing fee to be a percentage of the subtotal is not yet available in QuickBooks. 
 

Through our Feedback board, we can pass a request here about this feature. These requests and suggestions are forwarded to the Product Development Team, and I want to let you know that your voice matters, and each update our developer team creates are considered that it benefits our customer's business. 

Here's how: 

1. Access your QuickBooks Online company.
2. In the upper-right corner, click the Gear icon.
3. Under the Profile column, select Feedback.
4. Enter a brief description of your product suggestion, and then click Next.
5. Type your email address.
6. Once done, click Send Message. 

You can also visit our Help articles page for reference to find some helpful topics and discussions on managing your QuickBooks Online. 

I appreciate your patience as we work through this. If there's anything else I can do for you, please let me know. I'll be around to help you out. Stay safe!