This is a patch for the 2012 Nexus 7 Wi-Fi kernel to allow for host mode charging with an OTG splitter. I use this for my Kegbot (https://kegbot.org/)
The code is ported (and poorly at that) from https://github.com/mehrvarz/android_kernel_asus_grouper/commit/e35cc4de7f891cf71e206c72af4b0f61820f2fea. This patch should (mostly) just include what's needed to allow host mode charging from that commit. It could definitely benefit from a bit of clean-up and TLC.
There is a pre-built copy of the kernel with the patch applied on 6ff7a516ea0284e3265075001b91e6df3e16509f in the releases section. That kernel is verfied to work on Google's 5.0 Factory Image -- https://developers.google.com/android/nexus/images SHA1: 93daa4d30d7e9201f038591d8cfb9486c54e056d. It might work on later versions as well; I'll give it a shot once I download the latest.
Grouper source: https://android.googlesource.com/device/asus/grouper/
###NOTE
One caveat to notice is that, like the kernel this was ported from, you must plug the usb cord into the tablet last. That is, if you plug the usb cord into the tablet and then the wall or splitter, it will not work until you plug-and-unplug at the tablet.