I haven't read the Hawking paper in question specifically, but the idea of towing a worm hole around is that you move one end of a worm hole for some period of

I haven't read the Hawking paper in question specifically, but the idea of towing a worm hole around is that you move one end of a worm hole for some period of time at relativistic speeds. Since as you approach c, time slows down, so the stationary end of the worm hole is further in the future than the one that was moved around. It's a pretty stock layman's example of how time travel could be possible and I'm sure Hawking has torn a, er, hole in it some how.