You don't have to keybind, but it can work well. On mine I just turned off all of the automatic abilities, then clicked on the pet's action bar to make it do the sonic blast.
The automatic abilities like growl, cower, bite, and sonic blast will have a glow at the edge of the box if they are set to automatically trigger when enough focus is available and the cool down is up. Right-click, or Shift-click to toggle the automatic off and on.
Other tips: Many players never use Growl in PvP. Growl can be good to pull another pet off of you to attack your pet instead.
When you get a chance, dump the Bat and get a Ravager instead. They have a 40 second cooldown on
Ravage instead of the 1 minute cool down on
Sonic Blast.
The effects are very similar. To get a Ravager as Horde can be a long trip, but it is very doable. My only tip on that is: drown under the dock where you catch the boat to Azuremyst Isle, then rez on the stern of the boat.
Good Luck,
-Grey