Liberate_AMS, how to add RC load on transmitter PAD for lib

Hello everyone, 

  When I use liberate-ams to generate lib for transmitter circuit.  the output pad need add load cap and termination res of 50ohm. I can't find how to add this in the user-guide. 

 But in liberate, there is  define_pin_load to define the pull up/down resistance. 

How to do it in liberate-ams? 

Thanks 

Andy