The amazing PAR is indeed capable of handling XS Modules cross-platform. In order to create such a package, I would need to run the packager on each platform.

Unfortunately, for some reason I cannot get PAR to install on my university's linux boxes (I tried a local install and there's an error about insufficient permissions on ~/.cpan/sources. Oddly, the perms look ok to me).

Par files are essentially zip files, but I don't know whether it would be possible to add the multi-platform modules manually to the archive so that they work. You could manually create the necessary directory structure as it is described in PAR::Tutorial, but I'm not sure about the meta files.

Update: Happy New Year!