Hi, I don't know a lot about the cohoshes, but I can point you to an article discussing the pharmacology of blue cohosh:http://www.birthlove.com/pages/health/two_ways.html
This site is by subscription only (I think it's $10/yr) -- I'm sure you can do a search and come up with similar information elsewhere. Here's a summary of the article:
"Blue cohosh is a North American herb with a reputation for both causing and preventing miscarriage (abortion), but it is most widely known for its use in labour induction.
There are some unpleasant side effects from blue cohosh, including elevated blood pressure and blood sugar levels, nausea, severe stomach pain, and toxicity. There have been two case reports where blue cohosh was blamed for severe cardiac toxicity in infants whose mothers used the herb to induce labour. In addition, the plant contains a toxic compound which is known to cause birth defects in cattle."
In other words, like all methods of induction, cohosh apparently carries risks.
If it was me I would try some deep squatting, a lot of relaxation and meditation, and heavy sex/masturbation. In any case, if the midwives drop you from their care and you have to go the hospital, you can still refuse to be induced.