Customising an egg in daycare?

[Kopakura]

Basically, someone on a facebook group is trying to convince people that he bred and hatched a legit Ditto by leaving his solo ditto in the daycare overnight.

Of course, I know this is 99.999% likely to be utter crap, but I'm having trouble finding any way he could have inserted an egg into his daycare, there are no AR codes that I can find or anything.

He owns a legit cart, and plays on a 3DS if that makes any difference.

Is there a way to do this with Save hacking, or cheats in any way?

Sorry if this is out of place or anything, the first place I think of to come to for save editing is always here.

Edit: OOPS. Forgot to mention, this is on Pokémon Black.

[evandixon]

There's a instant egg cheat for Action Replay (at least for Gen 4).

That might do the trick. Or it could result in a nothing (Pokemon with ID of 0). Haven't tried it with one Pokemon in the day care.

[Kopakura]

Hmm that's possible, they did mention that they thought they had a Magmortar in their daycare. I'm guessing they may have done the insta egg cheat, not realising they only had Ditto in there, then hatched the egg and decided to pass it off as legit?

I may attempt to test this if I can.

EDIT: Yep! It worked! That's how he did it, thanks!