Pneumatically powered, lower limb exoskeletons provide high levels of compliant assistance to a user and add little on-body mass when the power source is located off the body. Such tethered systems are useful to testing the impact of control methods on a user’s metabolic performance and benefit from the pneumatic actuators’ simplicity of control. However, the pneumatic artificial muscle (PAM), a popular lightweight actuator, suffers from a nonlinear relationship between its contraction force, length and actuation pressure, reducing its output capabilities and complicating the design of exoskeletons that implement these actuators. This work describes a mechatronic lever arm system that extends the capabilities of a PAM actuated exoskeleton by configuring the moment arm, joint angle profile to create a torque profile specific to the designers’ requirements. A design optimization shows how the proposed system can tailor the exoskeleton performance without changing the simplistic, on-off pressure control. The specifications and the expected performance of the detailed design is described.