If they put him on the 10 Day DL today, we could replace him immediately with Diehl in the bullpen. I say Diehl because he is on the 40, is lefty and is a reliever. When it's Gray's turn in rotation they can bring up Santillan and send down Diehl (or maybe someone else not performing if Diehl does ok).
In essence Bell gets his 14th pitcher for a few days, we get a look at Diehl as a lefty option and we get to see Santillan in the bigs. Once Santillan pitches assuming things look good for Gray, you could make another move for a few days till Gray is activated.
No 40 roster moves required.
I kinda want to see that. I'm afraid we'll get the "we think he gonna be ready. Oops, he's not quite ready" thing.