What route will you take to get there?
I rode southen Indiana a few years ago on TRIRI. One day we rode from Lincoln State Park, near Santa Claus, to New Harmonie. I remember the route as being pretty flat. However, the 1st 3 days of the ride that week went to Spring Mill SP, Patoka Lake SRA, Lincoln SP through the Hoosier National Forest, and it was very hilly. A lot tougher than the hills on the Horsey Hundred.
I looked at Map Quest and I don't see any way you can avoid Hoosier National Forest.
The organizer of TRIRI lives in Bloomington and knows Indiana well. Maybe you could contact him and see what he suggests.