I bought the below switch covers for some dumb decora switches I wanted to leave on. I had been using them alone but waf wasn’t great. I then remembered the little plastic tabs that come with picos and stuck one to the cover. Now the switch is covered with a remote and everyone is happy.
I’ve been looking for a design that Could be 3d printed and would incorporate the two pieces into one but haven’t had any luck. 
I did find one to cover a toggle switch on Thingiverse, but the whole wallplate gets whats effectively a spacer, and frankly its ugly as sin.
Seems like it should be pretty straight forward conceptually, but I'm afraid I don't have any 3d design skills!
Your solution looks like it works, and it ticks the WAF box, so win win!
S
You know they make a pico wall plate mount for decora plates right? https://smile.amazon.com/Caseta-Wireless-Wallplate-Bracket-PICO-WBX-ADAPT/dp/B00JZRAFEA/ref=sr_1_16?dchild=1&keywords=pico+mount&qid=1591299910&sr=8-16
There's no plate to go on top of your existing dumb switch though.
You don't need one, you take the dumb switch out.
Unfortunately I’m not in a position to take the dumb switch out.
Download the Hubitat app
