There are a lot of halfway decent options. Ideally this is what you'd like to have for a truly good bullpen the ability to shuffle guys around when they inevitably struggle, but not acting like you are giving guys a quick hook. I think on an innings basis Thornburg's struggles are all of 2 starts in length. Still In addition to moving Estrada to the pen and calling up Nelson, they could just call up Fiers, Jeffress, or Mills. I kind of like giving Mills a shot, since it lets the team hold onto that depth, and if he looks good while he's up it gives his value a healthy bump, and if he struggles you just kind of move on and have lost relatively little.