erm... right what i would do is get some plywood and measure out the radious of the pillar then coppy it onto the centre of the ply then cut it out so you have got a hole in the wood, then decide how much you want your bellcast to protrude from the pillar. lets say 2 inches, so now marc another circle around the whole 2 inches bigger and cut it out. you should now have a ring of wood, you need to cut this in half to fit it around the pillar.
drill plug and screw some little bits of wood to the bottom of the pillar for your ring of wood to sit on (make sure it is all level and all the bellcasts on each pillar the same hight.
to fix the ring of wood to the little blocks of wood you will have to do it from underneath with little screws, NOT FROM THE TOP as you wont be able to get to them once rendered. (if they dont seem solid you could strengthen it from underneath with a bit of driwall adhesive.
now just render to them as you usually would and when finished take all the wood away the next day.
you can co further an add a drip member to the bottom of the belcast but i dont think it would be wirth it as it is only for a pillar.
hope this all makes sense and helps