Just because you don't have a blogger account doesn't mean you have to sign as "anonymous". Leave your name at least, it's a nice gesture. You don't even have to have a website link. Just leave it blank.
To do this: under "Choose an Identity", click "Other" and simply fill out the name field. Then leave your comment. That's it.

On another note, I like the idea of the emails being Cassie speaking through Frank... but it really could be anyone. How would he prove an email was his?...well, besides a screen shot of him being logged in. =/