How do I use a parallel mechanism in isaacgym?

[shitoujie]

As we all know, URDF, SDF and MJCF specify articulated bodies as a tree-structures without loops. In pybullet we can create arbitrary constraints between objects, and between an object and a specific world frame to connect the legs of a quadruped 5-bar closed loop linkage. So how can i expot a series machanism in urdf and use it as a parallel mechanism in isaacgym?

[shitoujie]

we can also use a dummy module to turn a serial structure into parallel structure in vrep