Emaggie,
looking at the picture, it doesn't resemble a column at all.
I suspect that the "bushy" growth towards the bottom has grown in a manner as does basal growth on many a plant. I would thin this out and tidy the upper growth, not with drastic pruning as you mentioned, but to make it look more columnal, if this makes sense.
With the lower growth as it is, the plant is concentrating most of its energy into that part of the plant, so by thinning it, it should give the same amount of energy all over.
Good luck, and i would be interested to know how you get on.