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)
There's a very short explanation and code samples for Python and some other languages at the Ubuntu app developers resources. For blueproximity the PyGTK example should fit.
You need some basic understanding of the GTK signal system