The project web site explains how to write custom checks and custom filters, but not how to write quickfixes for one's custom checks.
(I'm not exactly sure whether this is really a bug, or rather a support request or a feature request. My apologies if I'm wrong.)
Please notice that ECLIPSECS's quickfix mechanism has a serious bug, see ID 3022303.
Moving to feature requests.
Contributions are welcome, especially as you seem to be the first one providing custom quickfixes ;-)
Format would be a pretty plain html file in net.sf.eclipsecs.doc/base similar to the extending_*.html pages.
Let me see when I get around to doing it!