First you need to be rooted. Then there is a thing called Xposed Framework. You can find it here:
http://repo.xposed.info/module/de.ro...osed.installer
First you have to install the installer apk, but the one available on the site won't work. When you'll try to install it'll throw an error. If you go into description it will give you a link for bigger installer, which will work.
Second thing you need is Xposed Additions, available on play store:
https://play.google.com/store/apps/d...ed.additionsgb
Once you install both run the installer.apk and install. Then enter xposed additions and it will let you remap the buttons. It's kind of tricky to add the buttons on Lynx, because it constantly detects button 211 'wakeup', but if you press other button and instantly press OK you should be able to add the button you need.
Unfortunately it sometimes fails to work and the button will do the default action. That's why I currently have home on circle and default action on hold circle. When I had "recent apps" on hold circle sometimes it would turn off the light and then when I held it again it would bring out recent apps, making it hard to turn the light on again. When tap center sometimes doesn't work it's not a problem, because pressing it second time works. It might be possible to tweak xposed to work more reliably though.