EDIT: The multimod has been updated now. So just use that directly
I found a workaround for those who cannot wait for LightmanP to update the mod, and want to see the endings and scenes immediately:
1. Download
Universal Gallery Unlocker
2. You'll get 2 files: hard.zip & soft.zip. Copy the contents (_mods) folder from the hard.zip into the 'game' folder of FL.
3. Run the game, go to Bonus Content, and the 2 new endings should be unlocked.
4. But wait. Don't start seeing the complete ending yet. Play the new ending, but IMMEDIATELY make a save point when the ending starts.
5. Close the game, and delete the '_mods' folder from the 'game' folder in FL.
6. Run FL again, go to Bonus Content, and check if the 2 new endings are locked. They should be locked.
7. Load the save for the endings you made before, and enjoy.
Why so much hassle instead of copy-paste-play?
Turns out that the Universal Unlocker gives that "An exception has occurred" error whenever a choice is presented in the endings. If I choose to ignore the error, then the main character always automatically selects the 'decline' option from the choices. It kinda becomes a kinetic novel and you cannot select your choice of content that you want to see in that ending.
It can be fixed, and you can select any choice you want if you load the save after deleting the folders.