I've grown Jack Herer a few times, and it does stretch quite a bit in the first 2-3 weeks of flowering. It actually grew too high in one case and I lopped off the top buds and dried them for early use, leaving the remainder of the plant to finish in it's own time.

The early stuff was a bit harsh, (they didn't get flushed to clear ferts)but did the job, and the plant did just fine with the new top buds. I didn't want the bending, because I'm sort of tight on space all around, so it wouldn't have helped.