The point of hovering is to make some information available to the user about an element without triggering some primary action.
One approach might be to trigger the display of secondary information when dead space near an element is touched. That's not very discoverable though.
A better approach I think is basically the answer given above - touch and hold. But the first few time the user simply taps reveal the secondary information just before going off to the primary function, so that they know there is something to explore. It's not quite what 37 signals is saying though as I would not block the primary function, I would just reveal briefly it is there.
Instead of touch and hold you could also consider a swipe across something as seeking information, though again that's not easily discoverable unless you present an indication it is possible. I don't think there's anything wrong with the first few passes of an application presenting a few tutorial kinds of illustrations to let the user know something is possible, and many things like touch outside or swipe to reveal are very easy to remember even if they are hard to discover.