Well, what I need are the shared object files (except for networking) of SFML 2.2 built for Linux x64 with libglew-1.5 (or is it 1.6?) and libjpeg8d linked statically. It's messy, I know, but I failed to find a better way to solve those dependencies (e.g. Fedora does not have libjpeg and many systems only have libglew-1.7 or later).
Then the native part of JSFML needs to be built on Linux x64 as well (using "ant linux64") - the output file libjsfml.so needs to be packaged in the release jar.
I'll have to set up some VMs again to make it an automated workflow, but I don't look forward to the effort, especially since VirtualBox had a lot of problems with Debian 7 and/or my host system.