Ability to add text to input/text fields of default email body templates

As an example, when sending an invoice, you allocate a default email body template for the body of the email.

As templates allow input/text fields, it would be handy if you could add to these fields on the email body template when sending.

Using the invoicing example again, we would like to be able to personalise the message a bit to the recipient - collections being a sensitive area.

Is this something that is possible? Or is there any work around to be able to send an invoice template as an attachment through aXc while being able to customise the body of the email?