Wow, thanks for all the input! I took my bike to a local bike repair co-op and we were able to get the cranks off with a standard tool. It turns out I was being too careful of stripping the crank threads, and just needed to apply more force. Also I think the fact that the crank has a slight curve to it threw me off; I was trying to hold it perpendicular to the crank, but that wasn't quite parallel to the spindle.