To answer my own question, I finally found a solution ...
While there isn't any paste event you can catch a menu
command invokation for paste of a native menu. You need to add an
event listener for the SELECT event to the native menu.
Then you can either handle the paste yourself or call
standard functionality by invoking nativeApplication.paste()
You need a native edit (normally with at least cut, copy,
paste, select all) menu for that, preferrably with the common key
short cuts. It is automatically created on the Mac but you have to
create it yourself for Windows (haven't tried Linux yet, but I'm
sure you'll need to create it there as well).
By creating your own menu, especially on windows (where you
have to), you cut off all standard behaviour for cut, copy, paste
and select all, so you have to call the according methods of
nativeApplication yourself. If you reuse the standard edit menu
that's created automatically on OS X you do not need to do that.