I just realized that under 13.04 it isn't possible any more to add applications which are using the systray to a whitelist. I found the suggestion of downloading a patched version of Unity but I'd rather make one app I like (see bug report for blueproximity) use app-indicator instead.
I saw several python apps exist for application indicator, for instance ClassicMenu Indicator . So I want to try to adapt the program.
What I need now is a pointer where/how to start, maybe a few hints. (No experience with python but plenty with several other languages)