Google Cardboard Magnet Switch with Daydream Unity technical preview

TL;DR How can one build a binary for Google Cardboard, taking advantage of the "asynchronous reprojection and VR performance mode" but still have magnetic switch/button support? (and ideally also Daydream support -- but I believe Unity and Google are working on this part.)

I've just been trying the Daydream technical preview but am disappointed to find Cardboard support seems degraded. The SDK no longer supports the magnetic switch/button after rev. 0.9.0 (see "GVR SDK Release Notes" under v0.9.0 searching for "magnet"):

GvrView no longer supports magnet trigger detection or NFC-based pairing for v1 Cardboard viewers.

I used git to switch back to 0.8.5 (git hash 0970cdf44026031992022728375cd4bd1387d4f6). When I tried building I got lots of problems so I started a blank project and reimported, followed all the steps. However this gives error "Unable to convert classes into dex format" caused by "com.google.common.logging.nano.Vr" and its inner classes. I guess they're hidden in there somewhere but I haven't found them yet. Even if I do, I'm now using 0.8.5 library which likely won't integrate fully. I was only able to work-around these by disabling the Technical Preview's VR support (from Player Settings Menu). Obviously without that, I assume you totally lose the VR-integrated benefits ("asynchronous reprojection and VR performance mode").

If I want to resolve this, I'd imagine I'll need to find the magnet switch code in 0.8.5 (C/Java/C#), find its absence in 1.0.0 version and restore it. It's likely viable but work everyone with this need will need to redo. Will Google accept a Pull Request reintroducing this? I fear if they were to, they'd likely have kept it anyawy! Where/Who to pester to get it fixed? Or is it perfectly possible and I'm missing something obvious? (crosses fingers)

So in conclusion, I can use nice speedy Daydream Technical Preview but no Magnetic button -- a total killer if you want that extra control for the millions of Cardboards out there as customers. Or I can go back to pre-Daydream non-VR-accelerated version.

All thoughts appreciated. TIA!