Define then following macro, substituting Wolf and Spider for your normal and recovery pet, respectively:
#showtooltip Call Stabled Pet
/use Roar of Recovery
/use Call Stabled Pet
/run PleasePetBuff("Wolf", "Spider", "Roar of Recovery")
Then press it twice.
Inspired by NEXT PLEASE!! by Fluffydork: https://wago.io/6C0cpZUBW, but specially designed to apply Roar of Recovery (or any other pet buff, really). Together with the macro, this WA automatically swaps to the buff pet, casts the buff, and then immediately swaps back and closes the stables. Two clicks are required due to API limitations imposed by Blizzard.