64 bit support in L4Linux

Hi, I've a short question related to L4Linux for 'x86_64'. When looking at the L4-specific architecture-files, I got the impression that the 64-bit support from the x86 port got retained. But my attempts to enable 64-bit in L4Linux failed. (Setting environment variables, tweaking configuration, hacking Kconfig a bit...) Does that mean 64-bit isn't supported by now, or if it is, what is the recommended way to enable it? Any advice on approach is welcome. Thanks, Stefan