Until then maybe this works (besides the "webbrowser-trick"): I just found this Wrapper Application For Pandora Running In Task Tray and did not try yet - but maybe started from within MP it works well for playing pandora .
It works, you can listen to pandora with that application started from the EasyApps-plugin. Only the contoll with the remote is not fully supported so the (ir-)keyboard is necessary when exiting.