Is there such a thing as custom lightweight lenses?

I've been on a bit of a camera and lens tear recently, but the thing that I note consistently is that good, bright glass is heavy glass.

Here I am, with the Sony Z2 as my "everyday carry" because I object to carrying a heavy notebook - and then the moment I pack a relatively lightweight camera body with a decent lens, it feels like I have an anchor in my backpack / messenger.

Aside from carrying a ready supply of helium balloons to tie to luggage, are there any options on the market for drastically reducing the weight of top quality glass? Perhaps a pipedream but e.g. I'd like a Zeiss 24-70 2.8 which weighs somewhere close to a kit (i.e. <400g as opposed to >900g).