I've been around Marketo for quite awhile and I haven't found any reasonable way to do this. If you are sadistic you can check out Velocity scripting for emails here:
http://developers.marketo.com/documentation/email-scripting/, but even that probably won't do it.
I have our Blog Subscription as one program, and just send the email when a new post comes out.
Like I said in one of your previous posts, automation for automation's sake shouldn't be the focus. Only takes me 10-15 minutes to put together the email. Unless you're blogging multiple entries a day, I wouldn't bother with it.