Possible to have hidden part of mesh still viewable?

OK I’m hiding part of the mesh so I can use proportional editing on another part without effecting it, but I would like to still be able to see some kind of “ghost” of the hidden mesh so I can judge what I’m doing. Hope that makes sense. I’m sure there was a way I learnt years ago, it’s just disappeared from my brain.

Not really a “ghost mode” but: