Although maybe this approach is cheating because it's relying on https and not some kind of hash-linked P2P magic (which would definitely require modifying nix to make work). I guess there's something similar to the IPFS gateway going on: somebody is hosting a bridge into radicle space. It would be interesting to get this working without dependency on that bridge.
Anyhow, modify your project's flake accordingly and your version of `rad` will track with that radicle repo. No curl-to-bash required.