Bug #708180 in Application Indicators: “Indicators "scroll-event" support”
Source : go.3v1n0.net
Actually the only indicator which supports scrolling over it, is the indicator-sound. However libindicate support that signal for every indicator, but not for indicators (like indicator-application) which contain many other child entries.
After three days of work, here's my patchset for getting signals to an AppIndicator (Ubuntu)