Can I remove invoice value from email?

FiFiM

Is there a way to fully remove the value from the email and email subject when emailing the invoice? Therefore forcing clients to open the invoice attached to the email?

I need to know when my clients view the invoice (mainly so I know they've read it, but also so I know they've seen the additional info written in their invoice). Because the value is in the email, they're not opening the invoice, therefore I'm not receiving notification "Joe has viewed invoice".

Thanks