Hi Martin
I just pushed a change so that detect_lostruns takes in an optional argument called "launch_query". Here you can restrict any part of the launch document.
You should be able to set launch_query="{'host':'my_host'}" or launch_query="{'host':{'$regex': 'my_host*'}}"
This should be pushed in the next release of FWS (v1.9.3). I haven't had a chance to test it so let me know if it works for you.