Well, if you don't need anything flashy, just do it like all the lamers did with their packdisks back in the day, when the future was bright and Commodore wasn't dead:
Create a text file with the numbers and corresponding games in it:
1 - excellent game
2 - even better game
3 - this game isn't very good but my sister wants to play it
then in your s:startup-sequence:
type menu <- or what ever you named the above text file
cd sys:launchdir
now in sys:launchdir you make shell scripts that launch each game:
The following will have the name "1"
cd sys:games/excellentgame
assign excellentgame: ""
excellentgame
or what ever the game needs to get going.
Protect these numbered scripts SRWED so you don't have to use the execute command.
protect 1 srwed
(how difficult ;-)
Now, when you boot the machine, the startup-sequence first types the menu to the screen, then changes into the directory where your start scripts are.
Then you press 1 and the script called 1 starts and loads the game.
Of course you probably want to rename your original startup-sequence as something else so you can boot the machine normally when you want to..
And I don't want to hear you saying it's hard! It isn't, just do it one step at a time and ask for clarifications. In the same time you'll learn something about AmigaDOS.
Good luck! :-)