MEMBERSHIP PLUGIN: Negative Comments Rule and Call to Action to join

Hi, we have a free content blog and we want to gain members by requiring registrations to comment.

I've created a strangers level that is set with the negative comments rule (and only this rule), and have even modified membership-config.php to display existing comments, and the comment form is correctly hidden.

My question is simple - Is there an option in the plugin admin screens or the membership-config.php to place a call to action or link to to the registration form to 'Join Now to Comment' ? I sure don't see it.

Will I need to custom code this or is there an obvious solution that I'm missing? (I'm a real good assembler of features, but not at all a coder anymore.) Is there a better solution than this negative rule?

thanks much,