Hello,
WHMCS should have this as a basic. I haven't come across this not being populated with other purchases I make with companies. It looks very suspect to customers and they are reluctant to make a purchase when they can't see the product or pricing. It's like signing a blank cheque. I wouldn't do it so how could I expect customers to do it.
If whmcs won't fix it since the code is encrypted do developers have enough access to modify the code and fix it ?