I'd be quite happy to implement this feature myself, but I am not terribly familiar with how rustfmt works under the hood, and I wouldn't really know where to start. I could get a couple pointers in the right direction from a maintainer, I'll fork the project and try to add this feature.

@hawkw have you seen https://github.com/rust-lang-nursery/rustfmt/blob/master/Contributing.md#a-quick-tour-of-rustfmt ? I imagine you could implement this by changing code in lists.rs, unfortunately that is some of the more complex parts of rustfmt. Once you've had a look, feel free to ask questions here or on irc.

We are unlikely to support this, sorry.