Allow HTML in email notification of receipt

Hi All

Main purpose: make an automated invoice/receipt from the pro sites system after the subscriber pays.

Thinking solution: allow HTML in the email notification area so that I can make my own invoice-like html email to the client.

Can it be done? I see that pro sites says "No HTML allowed", is it possible to hire developer to allow this? If automated date, client info, running invoice number, etc can be included into the HTML then it would be best.