The use of remote excavators for disaster relief is preferable to the use of human relief workers. These autonomous systems are subject to inherent flexibility in their bases. Motion of the upper mechanisms of these systems induce oscillations in the base which feed through the manipulator system. To damp these oscillations the posture of the manipulator system is reconfigured so that the flexible modes of the system become passive. Stability margins of the system are characterized across the manipulator workspace and are used to inform the passivity of the manipulator flexible modes. Using Jacobian inverse nullspace augmentation, the redundancy of the manipulator base is used to pose the manipulator in a posture that is closer to passive. It was shown through simulation that the relocation of the mobile base of the manipulator to change the posture is successful in stabilizing the unstable open-loop system. Through posing the manipulator to maximize the stability margins of the open-loop system it becomes possible to treat the manipulator as a rigid system and employ simple state feedback for control.