So when you're lvl 79 and just before you ding 80, fill your stable with lvl 74 pets. Make sure you give them Bestial Wrath, Mend pet, Last stand (tenacity only) and any other pet buffs you have. And if possible, have other classes buff it as well. When the pet has all buffs you want on it, put it in the stable. Rinse and repeat for all your pets.
When you're level 80, you will now have 4xlvl 75 pets with buffs that lasts for several weeks, and it will be really easy to level them up to 80.
The buffs will last until the pet dies, or until you die when you have the pet summoned. They will not be removed if you dismiss the pet before you die. Keep that in mind if there's a wipe incoming.
Happy hunting!
by Tengu