As a temp thing, put this in your "~/.profile" file:
alias piholepass='sudo pihole -a -p $(whiptail --title "Pi-Hole" --passwordbox "Password" 7 30 3>&1 1>&2 2>&3)'
Activate without rebooting by running:
source ~/.profile
And use "piholepass" command/alias to enter password (or leave empty) without being displayed on screen.