I'm not sure if I'd be able to ride, having work and all, but I'd love to if I could work it out. I've also got this nagging achilles issue that's kept me from riding much the last 3 months, so my fitness level isn't great...but it's just 100 miles right?
The Collin Classic isn't far from where I live and it has a 52 mile loop.
http://www.collinclassic.org/routes.html. It's kinda nice riding a marked course.