Yes I know you can use composer create-project to initialise new repos. I like to use this system so that I can add to existing composer.json files.
Add the bin to your $PATH directory:
export PATH=$PATH:Skeletons/bin
There are scripts in the bin directory that will set up the current directory with your chosen skeleton, i.e. 'silex'.
Hack away!
Enjoy.
The script(s) make use of the jq command to edit composer.json files. If you're using Homebrew you can install it with
brew install jq
I am quite sure there are many other ways of installing jq :-)