Raise the roof!

One of my plants went through a huge growth spurt while I was away and is about 10" from the ceiling of my G-house. The stem is firm and I think that supercropping is out of the question. How much can I cut off this beast without harming the plant? This is the only strain of SC I have in this grow. The other BC's are about 3 feet tall and this one is about 6 feet. I need to plan for flowering too as it will shoot up again. Should I cut a foot off it and then repeat as needed? Or hack it down a couple feet right meow and lst the new growth? I'll get a pic up when I get home.

Thanks peeps.

Here's a fresh pic.