You don’t need to. Just replace the power switch with a blank panel and stick the wireless one on top. The battery should be good for more than two years depending on the usage.
That’s probably the only way if you don’t have neutral and want the lamps to be always on. What I do is have one smart wall switch in place and have an additional round wireless switch at my bed side. The lamps operate as usual and can change colors when they are powered. The wireless switch is tied to an automation which toggles the wall switch.
That could do it. Thanks a lot =)
Still, is there any zigbee wired switch that could be used ? That would help to enhanced my zigbee lan.
Without a neutral you are probably out of luck 
Why would you want a controlled switch there if it is feeding a Yeelight though? Any time the switch is off the light will be ‘unavailable’. I would simply hard wire the switch ‘on’ and use a wireless button.
I’m coming late on that topic but there is also a possibility of making the Wall switch work as a Wireless switch through the option “convert the button to a wireless switch” in the settings.
But for some reason I never managed to make it properly work : Disconnection of the switch from the network, relay of the switch popping out when turning the light on “logically”
Did anyone tried and made it successfully ?