Sorry if this is a repost... grow Diaries be actin funny.
Personally, I would choose methods that reduce stress.
Raise your fixtures, add a fan on them to keep ballast cool and this will help prevent your plant tops from burning as well.
You can then gain a few more inches by placing a trellis above and slowly working it down over time.
Try to focus onspreading the tops towards the inner walls of the tent from center point. That way if they do continue to grow, they might be able to grow above the fixture.
With my current grow, where I ran into a similar issue, I researched as many possible solutions and there was one I wasn't able to try which was running straight blue lights until stretching has ceased since I didn't have any readily available.
As far as dimming... I didn't. Fans on the lights and ballast worked miracles on preventing burn. Plants are much more robust in this stage. I just kept an ever watchful eye on them.