Quick answer: you don't use Bower for that.
Bower is a package manager and will grab the distribution as the author defines it. You can define the location where it saves the packages but not cherry pick individual files.
You are missing a build manager / build script that can (among other things) copy files from one location to another. By far the most popular are Grunt and Gulp.
I would highly recommend taking the time to learn and integrate one of these tools into your workflow.