Editing /usr/lib/chromium-browser/default and adding the ppapi string didnt help (see respesctive Thread @ ubuntuforums.org).
So I called the iron binary directly with the parameters - AND it did work. This means that iron is probably not called via some shell wrapper file (eg. the chromium-wrapper shell script being supplied within /usr/share/iron). Instead its .desktop application file calls the binary directly, thus ignoring any possible additional settings.
a) Use the chromium-wrapper shell script to call
b) Create a wrapper script that adds the parameters directly to the binary call
c) add the enviroment flags to the local equivalent of .bash_rc
Gonna try them and report back as soon as I got it working.