Retrieving id's of an async relationship

I have a number of situations where it would be very beneficial to access only the supplied ID’s of an async relationship without going off and fetching the full records.

For example, each User has an async friends relationship, with the server supplying the ID list. I would really like to be able to compare the ID’s of the friends relationships on two User models to obtain a mutual friends list.

Is such a thing possible with Ember Data?