Rooting Hormone - Should work, if you pulled the plants, applied the powder or gel and allowed some time out of the tank for the rooting hormone to be absorbed into the cutting site. It works by being drawn into a fresh cut and being absorbed by the plant at the 'wound' site. Same goes for trimmed roots.
I would pull the plants, make my cuts, apply the powder, wrap in damp paper towel, and place in the veggies drawer of my fridge for a few hours. Then replant.
The cool damp environment will allow time for the rooting hormone to be used by the plant without undue stress to the plant.
Adding it directly would have a very low probability of working.