I use Zurb Foundation along with Susy grids, they both have a mixin named "prefix". I'm using "bower" to include them in my project, so how to namespace them without changing in their source code?
I can imagine only a not so clean way:
if you can separate the .scss that is using Susy grids from the other foundation stuff, you could use grunt to compile 2 separate files, one sass run for foundation and one run for Susy grids, then eventually merge the 2 outputs.