Moved this post to the Web API board for better visibility.
I don't believe this has been implemented, my understanding is that the currently supported ODATA operations are:
$top - The maximum number of items returned in each page. $skip - The number of rows to skip in the result set before returning results. $filter - restrict the result set based on Query criteria $orderby - Specifies the order of the result set
I'll forward this thread to the web API development team to confirm.