God, hearing the sounds Ianto was making alone would probably be enough to bring Jack off on their own if he were less in control of such things. As it was, though, Jack found himself wondering if maybe he could get Ianto going even more. And so, though he kept his hips rolling in time with Ianto's, as much as he could while he was lying back like this, he stilled his hand on the other man's arousal, just holding on, his grip loose enough that if Ianto wanted to do the work himself and thrust into his hand it would create all the delicious friction that the other man desired, but Jack's hand itself wasn't moving at all. He was going to make Ianto work for this one. The other man had challenged him to tire him out here, after all, and Jack was never one to back down from a challenge in bed.