Local storage for Shadertoy wallpapers

I've got a slightly flaky internet connection, sometimes there's issues when starting up, and delays when switching between wallpapers which use shadertoy.

It'd be nice if it were possible to store these wallpapers locally. Ideally, lively would cache a copy, preferring a live version if/when it's available, with a setting to change this behaviour on an individual wallpaper and globally - options could be cache and don't try to get live, cache but prefer live, don't cache at all