Problem with SetStopCondition

I want to ask you whether it is possible to set stopcondition for axis_x and axis_y?

the two joints axis_x and axis_y (ros joint names) of the two linear axes are simulated without force sensors. because there is no force measurement there is also no way to set a force based stop-condition for them.

StopConditions of condition_type == "joint_ext_torque_threshold" can only be specified for the lwr joints and the gripper joint. (ros joint names:
lwr_joint_1, lwr_joint_2, lwr_joint_3, lwr_joint_4, lwr_joint_5, lwr_joint_6, lwr_joint_7, gripper)