How can my little sis trade her pokemon from one game to an other with only one DS?

I know this isn’t possible,

We only have one DS, and a copy of Pokémon Diamond and Platinum,

And want to trade all her favorite Pokémon from Diamond into Platinum before trading Diamond in to game stop for credit toward Soul Silver

After that she wants to I’m sure, trade them into Soul Silver

It’s all becoming a big hassle, and I want to figure some kind of solution for her dilemma before or around her b-day this Friday

What can I do?

Will Game Stop help me trade them over with one of their demo DS’

Are there some trade networks in Minneapolis, we can meet with for help

Is it possible to trade between one of the Pokémon Wii games (which we can rent from Game Fly) and the DS?

Thanks for the help

Much love