The point is that first launch has no serious interest to warrant a real payload due to the higher risk of failure. If they weren't doing something fun like this they would just be loading it up with dead weight.
[1] https://en.wikipedia.org/wiki/SpaceX_COTS_Demo_Flight_1#Addi...
You'd also need some kind of deployment system.
I'm also fairly sure Musk has already considered doing this, and reached a conclusion that it wasn't feasible.
Do you have evidence of this? Or is it just a hunch...?
Although I guess you could argue this one does too, given that it's not from the production line, probably hand-built.