Exclude read-only messages in REST search?

I've built a custom component to show the last 5 topics without a reply (More details on that here: http://lithosphere.lithium.com/t5/developers-discussion/Threads-with-no-replies-Skip-to-end-of-metadata-Freemarker/m-p/23880 )

 

If recently a lot of messages have been moved out of a board where this component is used and "Moved: " placeholder messages have been left the whole "Topics without replies" list is filled with "Moved:..." topics. Bad.

 

I'm currently using this REST search call to get the list:

/boards/id/${coreNode.id}/search/messages?openresponse=true&sort_by=-topicPostDate&page_size=5

I was looking at the messages in the return result but can't find a way to tell if a message is just a placeholder message. The closest I cant get is

<read_only type="boolean">true</read_only>

 ...because placeholders are read-only by default.

 

Now the only challenge is finding a way to filter out read-only messages from a REST search call. According to http://lithosphere.lithium.com/t5/rest-api/bd-p/developers-rest-api?leaf-id=Board.search#Board.search.messages (which btw. misses documenting the "openresponse=<boolean>" paramter) there's no such option. Anyone knows a clever way to do this?