As it is quiet I thought I might see what people think, there are a lot of "how to train" gundog videos on youtube but much of it to me appears to be training for trainings sake and have little to do with practical gundog work or even trialling but I suspect teaching the dog something in a certain way either because you can or because the trainer believes or expects the dogs have little natural ability or desire to work.
Here is how to teach a dog to pick up cold game
https://www.youtube.com/watch?v=4kNbB9ycFDA
Even my poor retrievers over the years have been keener on game rather than dummies and I am sure many out there have resorted in giving a dog cold game rather than a dummy at some point to encourage it to carry.
All of the better dogs have already picked cold game by six months old, either by design or often inadvertently by them finding something dead when on exercise and bringing it to me.
I am not sure I really see why you would go through all this when you could just see if the dog wanted to retrieve it by putting it out as an easy retrieve.

If the dog isn't interested then you have a problem but I would not be overly keen on a young dog who didn't want to carry up a partridge, it might find a cock pheasant a bit big if the dog is very small. I would expect a youngster to be rather more interested in the partridge than a treat!
How do other people introduce cold game?