You can install onto Gotham builds with this repo:
https://github.com/popcornmix/repository.popcornmix.storage/raw/master/repository.popcornmix.zip
Download the zip file and install from setting/addons.
And then install from the new popcornmix repo the screensaver and visualization.
Select shadertoy screensaver in appearance/screensaver settings
Select shadertoy visualisation in music/playback settings
You can change the screensaver preset in screensaver settings.
You can change the visualisation preset when music is playing. Switch to fullscreen mode, bring up controls (enter) and select preset (rightmost “mountain” control in confluence).
Edit: updated instructions to use the repo, so add-ons will automatically update.