You could still go with more of a cyclocross type bike, use 35 mm wide tires and a flat bar. It's not that unusual for a people to ride flat bar cyclocross bikes. Or I would consider a bike like the Rove but with a rigid fork, instead of a suspension fork. Suspension forks are heavy and require maintenance. With the kind of riding you're planning on doing, it's not really necessary. Though to be honest it might be nearly impossible to find a mountain bike type set-up with a rigid fork.

Though I loathe to recommend Specialized (for business ethics reasons), have you considered something like this?