If in need of keeping them short, why did you chose a sativa dominate strain?
If you are really short on vertical space, I'd FIM the crap out of 'em, and put them under 12/12 a little early. You may still have to tye-down rogue branches in flower though...depending on the strain's propensity to stretch.
Fimming will cause some injury that delays growth, which will add a couple of weeks to the harvest date.

I have plenty of headroom and I prefer not to FIM, but it can be an effective tool if used right, for the right reasons.