I saw a youtube video, I think posted here, of a batsman giving fine edges to a keeper standing up at nets. I first tried to replicate this using cardboard but it only lasted a session so I found a bit of bathroom floor vinyl and glued and screwed it to a thin 'technique' bat.
IMG_5872.jpeg
IMG_5873.jpeg
The cardboard worked well other than its longevity. It allowed the dummy batsman to play shots and get fine edges without them being so thick that you stood no chance of catching them.
This a video from nets
https://youtu.be/QqgulcWilVE if you go to 12:43 and put it in 0.25 playback speed you might see a bit of an edge.