Phoenix has a "de-render" option that allows you to derender objects or other people to your view.
Phoenix's dereender is persistent across sessions, the version Imprudence implemented was session specific: you log out and back in, and the object would be re-rendered. (I like the per-session version myself, but that's just me...)
It's really useful when your neighbor decides a 50m tall by 50m wide neon SUPA-GLOW FULL BRIGHT box is the perfect landscape addition.... *twitch*
That is what I suspect the OP is looking for.
(and if you want to complain about spying, honestly, alt-cam does a lot without any real effort. De-render not necessary.

)