These are the config files and the save files for running individual levels on the leaderboards.

Put the configs into your valve folder. Put the Saves in your SAVE folder.

When you are in Half-Life, execute the config files by typing "exec <CFG-FILE-NAME>.cfg", which brings you before the first map of the individual level.

Go through the changelevel trigger to start your run. Finish the chapter, and the Demo will automatically finish, so you can submit it to the Leaderboards.

Thx to KaNanga and nyddesson for coming up with the ideas to setup ILs like this.