Mapping between PWM counts and joint angle in ros_canopen

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I'm using ros_canopen, which is an awsome package, to communicate with my robot.

By far, I modified the below yaml parameters to deal with the mapping between PWM counts and jont angle.

default:
  pos_to_device: "rint(rad2deg(pos)*1000)"
  pos_from_device: "deg2rad(obj6064)/1000" 
  vel_to_device: "rint(rad2deg(vel)*1000)" 
  vel_from_device: "deg2rad(obj606C)/1000"

Is there a way to use transmission ratio in URDF and define only a parameter of encoder resolution in the above yaml?

Thank you in advance.