Well, the videos of the events show the steps and choices required to view them, so...how to add new events to joiplay
If you know how to debug the game, you can find the corresponding maps and just slot them in. You'll have to create the maps that currently don't exist and implement a good deal of features in them AND link them to the main game, but it's not technically impossible.
Impractical, yes. Nobody would play this bootlegged update, almost certainly. But not impossible.
If you possess that level of skill though it's probably just better to do a text-only RPGM game, make a few bucks yourself. The Poor Whore, for example, is text-only and has literally no CGs, but its versatility and well-written scenes makes it a game I still replay from time to time even now.