It doesn't look like there's a .cbplugin file anywhere to add it separately. I was able to get it to build and install by installing the "devel" package for wxGTK2.8 in my package manager and then running make and make install in [source directory]/src/contrib/wxSmith
Once I did that, it added libwxsmith.la and libwxsmith.so to /usr/local/share/codeblocks/plugins. I still had to jump through that extra hoop with all the dependencies installed, and the binary package in my distro's repository didn't include wxSmith either. Bug report, maybe?