One way is to edit the files yourself.
I've done this, but only for the front page. (Added some favourite games below the A-Z buttons)
Another is to download the entire whdload game sets from this thread
Turrans game packs up to v2.3 have AGLaunch files included for the full game sets.
And finally you can use Solo761's tool
to generate AGLaunch files for any game set.
Edit: It's possible to set up any workbench (including BetterWB) so that AG-Launch will be launched by pressing a button during boot.
You need a small program called Getmouseinput, and set it up in s:startup-sequence. If you have a look at any classicWB install you can probably figure out how it works.