I took some castor oil when I was pregnant with ds. I was doing a homebirth and was in labor and not progressing quickly (I had been at 4 cm for almost 24 hours) and my midwife gave me a castor oil shake to see if it would help. To be honest with you I didn't find the experience too unpleasant. The castor oil itself had no smell or taste (I've heard that most people have a problem with the thickness of the oil). It didn't make me vomit or dehydrate me. It did give me diarrhea but that passed pretty quickly (I tried to look on the bright side and told myself I wouldn't have to worry about going to the bathroom while I was pushing
Some people worry that the castor oil passes through the placenta and can cause the baby to pass meconium (which, I'm sure as you know can cause problems if aspirated). My ds was born about 20 hours after I took the castor oil and he had not passed any meconium. Another caveat is the possibility of dehydration, but from your post you seem to be planning to take precautions to prevent that.
As for your situation, I would be scared to take castor oil then have to drive myself to the hospital. For me it kicked in pretty quickly and I had to use the bathroom A LOT for the first half hour and then the contractions came on hard and fast, so I don't see how that would help you in getting yourself to the hospital. If you would have to be driving yourself if you induced yourself or when into labor naturally, I would much prefer to be driving myself with my labor progressing naturally and without castor oil diarrhea.
I'm sorry that you have to deal with so much of this on your own and I hope this helps no matter what you decide.