I get curious as to how much development stuff I can do with OS X from time to time, as, though they are not twins by any means, linux and darwin are definitely cousins. Obviously the simg2img and make_ext4fs binaries in their normal state won't work on any darwin system (os x), however, they ARE unix binaries, and darwin is well... unix
So I downloaded the source code and compiled natively on OS X using xcode / gcc. When compile is done (didn't take long) dropped in /bin and.. viola! Works perfectly.
For those who want a tutorial on how to use these binaries, check here.
To mount sys.raw:
install either macports or homebrew. Then:
Macports: $ sudo port install ext4fuse
Homebrew: $ brew install ext4fuse
After which, cd to the directory you created sys.raw using simg2img.
$ mkdir sys
then, mount with:
$ ext4fuse sys.raw sys
and viola! it's now mounted and you can do what you will with /system
Homebrew: OS X package manager