This seems to freak people out... but I've literally just snapped the stems sideways and layed them criss-crossing on top of each other when the stretch got out of control... The obvious knee jerk reaction to this: "your plant will hermie if you stress them out too much" and I may be the exception to the rule but I've done this with great success, have had no hermies, and the plants never skipped a beat. In fact, after the first time I snapped the stems over... they stretched another 2 feet and I had to snap them again!
Of course, I'm not promoting this practice, just trying to ease your mind a bit. When you train those tops... do try and be gentle, but if one just happens to snap... don't sweat it.
*** Edit. Added photo:
A few days after snapping this stem: