For anyone interested, Thomas has contacted me to let me know he wrote a "Video Contact Sheet Ruby" which reuses part of VCS' code and outputs contact sheets in the same style.
Being written in Ruby, its code will be less of a mess and, even more interestingly, it can run on Windows with less hackery than VCS.

So you're invited to take a look at his project at https://github.com/FreeApophis/vcs.rb.