How do I create a work-item using REST API with a list of subscribers known in advance ?

I am interested in creating a work-item via REST API as described in this article using XML payload. (I was able to convert that example to use XML instead of JSON as shown in the article.) When I look into the XML of an existing WI (using https://HOST/jazz/oslc/workitem/9999.xml), I see that the list of subscribers is chained to another URL with the WI number in the URL. I am unable to post the URL as it gets whacked out when I submit the post.

When sending the POST request to create the WI, I wouldn't be knowing the WI number in advance, obviously.

This is at RTC 3.0