How to set the Person and Company ID on a comm link using the REST API

Hi 

When using the REST API to insert into the communication table it looks as if a default com_link record is created but it leaves the cmli_comm_companyid and cmli_comm_personid as null.

Is there a way to set these as part of the post to the communication or does a comm_link record need to be inserted that sets these values?

Thanks