Did a search and only find a guide where it is explained how to make the pets und that you should skill up your profession with them....
So yesterday i made some De-Weaponized Mechanical Companion - Item - World of Warcraft to make a little money (they sell for ~1000g at my Server). Then i switched my specialisation from Gnome to Goblin with the book in tanaris and learned Personal World Destroyer - Item - World of Warcraft to make a little more money....
Today i realised that i can make both cataclysm-pets while beeing a Goblin-Engineer.
You may ask: Where is the exploit, it is working as intended....
Answer: No it´s not! You can learn the De-Weaponized Mechanical Companion only as Gnome-Engineer and you can learn the Personal World Destroyer only as Goblin-Engineer. No ther Gnome-feature is left in my profession-book, i´ve unlearned all of them but not the companion.
So, switch specialisation, learn the other pet and profit...i can make 500g profit with each sold pet.
I really hope it´s not a repost, but didn´t find anything similar.
If it´s new and it helps you: Enjoy ;-)