Install packages:
sudo apt-get install xbindkeys xsel xdotool
Create xbindkey configuration file:
# ~/.xbindkeysrc
"echo -n | xsel -n -i; pkill xbindkeys; xdotool click 2; xbindkeys"
b:2 + Release
Set xbindkeys to load on startup:
# ~/.bashrc
xbindkeys -p
Log out, log back in, and you should be all set. If you are impatient, simply run xbindkeys -p
Never mind, I preemptively removed + Release after hearing it causing issues for Kvothe, but adding it back fixed it. So THANK YOU for providing the first working solution I've found after days of searching. I hope other people with this issue find this.