I've also read that you shouldn't do it.....you'll end up with diarrhoea and that's about it. My friend tried it along with curry and a bumpy ride on a road but it didn't work.
On a side note, her husband also took the castor oil as a show of support (silly man!) and when he reached the curry take-away place, he had to run straight in past the counter, to the toilets! Hehehehehe!
Good luck, hope bubs comes soon! I hear acupuncture works wonders....and you don't feel a thing (somehow!).....