Aren't these 2 separate requests?
1. No it isn't possible to drag and drop sprites like Unity sprites or indeed modify tk2d to do it while still being backwards compatible.
2. For draggable sprites in the scene you can use tk2dUIs draggable sprite. Check UI demo 1 for an example - thats a button, but the behaviour can be attached to plain sprites and doesn't have to be on a button.