People seem to be having a problem with this so I'll see if I can explain it any better.
What is needed:
A clockwork rocket bot for yourself
Another player with a clockwork rocket bot
Instructions:
1) Have your friend summon his clockwork rocket bot.
2) Stand in range of your friends clockwork rocket bot.
3) Summon your own clockwork rocket bot.
4) Your friends clockwork rocket bot will fire missiles at your pet. Watch the rockets travel and as soon as they hit your clockwork rocket bot summon a different pet.
5) If successful it will allow you to summon a second version of the new pet you summoned. If unsuccessful it will only let you dismiss the new pet.
6) For more pets, dismiss your second pet and repeat steps 1-5.
Tips:
If you stand ~20-25 yards away from your friend you can summon your clockwork rocket bot and have it killed 100% of the time without your friends' pet dying.
Watch for the rocket animation hitting your own clockwork rocket bot. The timing is hard to get right but once you know what you are looking for it becomes quite simple.
To make things easier, set the clockwork rocket bot and the pet you want to duplicate as active battle pets or as favourites so they can be easily right clicked and summoned.
Hope this helps people. Please let me know if anything is still unclear
