I do not get why you don't want to use Toornament/Battlefy/Smash.gg that would make running your tournament kinda easier because it does the heavy lifting for you. If you want to run the tournament in a weird config they don't give you, you could just create a fake tournament just to loot the codes from the lobbies.
I've found some tools online to generate the code like this https://www.reddit.com/r/leagueoflegends/comments/2z8xwr/release_lol_tournament_code_generator/ (Cant test them, League is down)
But at the end of the day, if you do not want to use a site to generate the code, I'd say you will be screwed to have a sheet of the exact setup you need the games to run on and then have the players or a ref (that then just throws itself as a spectator on the first occasion) create the lobby and then setup the game on the setup you want, and then run the game like any custom game. The tool I've shown has that as a problem. Even if the code works, you would not have any 'post game page' and so you are stuck at using your players word that it went like they say it did.