may it's because lzham isn't supprted by xz format?
anyway, the home of this project now is
https://github.com/mcmilk/7-Zip-zstd
and there you can ask (by creating Issue) author how to use lzham in stream mode, may be with other utility
also, as author of freearc, i want to ask you - is lzham really has its edge? i thought that it's barely faster than lzma while providing much less compression ratio. how frequently it's used in repacks?