Hi Michael, MSP 2013 provides the Path functionality that may help you to identify the driving path for any particular task in your schedule. That may suit your need quite well.
If you are on MSP 2010, then you might be interested in BPC Logic Filter (http://boyleprojectconsulting.com/Software.html). We originally developed it for internal use and then converted it to a Project Add-In to share with our clients. In general, our tool views the Critical Path as just another (special) case of the Driving Path for any selected task in the schedule. It also handles Path Relative Float (i.e. days away from driving), Driving Path Drag, Bounded Network Analysis, and Cross-Project Links (within a master/subproject hierarchy).
Have a look at the references on our site, then send us an email if you want to join the closed beta.