On LuxRender site has been announced that a fully integrated version of the exporter addon is available to download.
LuxRender team wrote:
Despite Blender 2.5x being still in heavy development, there is already a full integration of LuxRender available for it as an addon. During this development phase, the easiest way to get hold of a copy is to grab a pre-configured bundle from graphicall.org.
For instructions on how to manually install the addon, please see the LuxBlend 2.5 installation instructions wiki page.