See this little video I made for you. Click on the link below to go to a screencast video – don’t worry about the message about adobe flash if you get one, you should be able to view it:
you have to right click to add a newel and position your marker where you need the newel to be approximately. It will be added as a intermediate post. After it is added you can remove the first newel and position your new newel more correctly by change the absolute value.