"Have him use it to save someone," the Doctor replied, just a shade of desperately. "The Sontarans are working on destroying a nearby system. If he can stop the Sontarans, he'll save all of those people. It's not much, but it's a start."

It's almost nothing, though. The Valeyard will do it selfishly, to gain power. The Doctor would do it just to help people.

"You're clever, Master. You'll work out a way to get him there. You'll manipulate it."