Can't search for presence/absence of more than one subscriber

In choosing a set of bugs for the Desktop Team to work on each week, Daniel Holbach excludes bugs that have either ubuntu-main-sponsors or ubuntu-universe-sponsors subscribed to them. He achieves this with a Python script (hugdaylist, in the ubuntu-dev-tools package) that screen-scrapes Launchpad, visiting each bug report in turn to get its list of subscribers.

Launchpad's advanced search form lets you search for the presence of one subscriber. It doesn't let you search for the presence of more than one subscriber, or for the absence of a subscriber, and perhaps these are too obscure for showing in even an advanced search form. However, it should be possible to do this without screen-scraping, using advanced operators in the search query. For example, Daniel's filter could be represented by "-subscriber:ubuntu-main-sponsors -subscriber:ubuntu-universe-sponsors".