This is my overlay/extension of nixpkgs, with a binary cache. It's built from this github repository by using travis-ci and it's deployed as a github pages.
And for now, it's mostly an example of how to do just that. More details here.
To use it, add the channel and update it:
nix-channel --add http://www.lpenz.org/nixpkgs-lpenz/
nix-channel --update
To use the binary cache, you have to add its URL and public key as a
substituter in $HOME/.config/nix/nix.conf:
substituters = https://cache.nixos.org https://www.lpenz.org/nixpkgs-lpenz/cache
binary-cache-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= lpenz.org:jYDkTN/2qS96NxFnJpuWkNdVfNaWzaA5pmcg4MyXa2g=
You can now test it by installing execpermfix:
nix-env -iA nixpkgs-lpenz.execpermfix