Hi
Sorry, use the open source driver (you already use free or at least open source softwares including JOGL and GNU Linux). If AMD doesn't wish to implement a fallback not using DRI2, you won't be able to solve your problem. I don't want to debate about drivers under GNU Linux but using proprietary ones isn't viable on the long term because you're dependent on the decisions of GPU manufacturers motivated by commercial interests. Most of my computers wouldn't have worked for years without open source drivers.