In your flake.nix you can import a module that adds your options (can also just directly add but a module is probably cleaner):

{
  inputs.flakelight.url = "github:nix-community/flakelight";
  outputs = { flakelight, ... }:
    flakelight ./. {
      imports = [ ./nix/flakelightModules/my_module.nix ];
    };
}

Then in your module file, you can add options and config using them (same as for nixos or home-manager modules but setting the flakelight options):

{ config, lib, src, flakelight, ... }:
let
  inherit (lib.types) lazyAttrsOf any;
in
{
  options = {
    hosts = mkOption {
      type = lazyAttrsOf any;
      default = {};
    };
  };

  config = {
    nixosConfigurations = fnThatConvertsHostsToNixosConf config.hosts;
  };
}