Regarding the castor oil, are you at all constipated? Sometimes taking a SMALL dose of castor oil to help with constipation is enough to get things moving. I took 2 tsp just the other morning to help with some major constipation that I was having. 2 tsp was just enough for me to allow for me to have one GIANT (and very healthy) bowel movement, and absolutely no diarrhea.
There are many things that can slow down (or stop) labor, constipation being one of them. Long hot baths, and sometimes even laying down, are a couple others.
I'm a firm believe in letting the BABY trigger labor. Get that head nice and low to put pressure on your cervix. Ripen that sucker up naturally (or with the added aid of EPO or sex). If you induce before your body is ready, it can often lead to very long, painful labors, with an uncooperative (unripe) cervix. The bottom line is unless your cervix is ready (soft/thin, and dilating), the baby's not going to come out.
My suggestion is to do everything you can to prepare your cervix before attempting any type of induction, and then use gravity to your advantage.
As for the membrane sweep, I had 5 with my first child, and she was still 13 days past due (and she was planned, so we KNOW the date of conception). I also ended up with an emergency c-section after 26 hours of hard labor.
My waters broke after drinking the cocktail (I was desperate but still only took half of the recommended dose and ended up in the bathroom for hours anyway - NOT fun), but STILL didn't go into labor and ended up having to be induced at the hospital anyway. That said, I do plan to have it done again at LEAST once with this baby (I'm due on the 21st, but am in a LOT of pain - early would be better).
Just a warning that these things can sometimes work against you. But they're worth a try! GOOD LUCK!!