I'm thinking Lestrade puts him on a timeout or something, but forgets about him? Or maybe Sherlock stole Greg's cuffs, John finds out and as punishment has him wear them for some time? Something along those lines. And he can't get out cos the cuffer made sure to remove lockpicks, keys etc.
In short: Sherlock's hands are cuffed (preferably behind his back) for a fairly extensive while, and no sexytimes happen during it. How does he handle it?