The only lzma installer solutions i know about were kinda custom builds. A default osx installer with embedded 7za binary for extraction and a seperate lzma archive that is extracted using a postflight script. I wouldnt expect an lzma integration into osx, therefore the installers wont support lzma. All you can do is embedding the binary and control extraction using package scripts. One thing is shure, once you experienced the excellent solid compression ratios of lzma on executables you'll never use anything else ;) results are even better than using nsis on win.
Create the metapackage, add install options, build. Add the lzma binary and archive(s) to the (meta)package folder(s) and handle the extraction inside the package(s) postflight script(s). You can adjust the real install sizes in kb editing the integer value of IFPkgFlagInstalledSize Info.plist inside the pkg folder.
A side note: if youre after compressing audio samples, lzma isnt the preferred choice. Gzip and RAR a way more comfortable for this purpose, and way faster.