Just my two cents here. If you would change your build-system to CMake, you could use the CMakeListsCustom.txt files to achieve the same thing. You would not need to script anything, and could directly just copy the necessary file into the build. The plugins and additional dissectors do not need to reside even in the same src code database as Wireshark.
Take a look at CMakeListsCustom.txt.example for the reference.
Currently the customization applies to:
./CMakeListsCustom.txt.example
./epan/crypt/CMakeListsCustom.txt.example
./epan/dissectors/CMakeListsCustom.txt.example
./ui/gtk/CMakeListsCustom.txt.example
regards
Roland