My dad ended up doing the routing on this one, although I had planned to do it - he had some spare time on his hands as he couldn't drive for a week. He used a combination of bits of hose nailed to form a guide, free hand and I think he made a pivoting plate that allowed him to do some of the circles. The routing strips we used on our big track weren't flexible enough.
My idea and I am not sure if it would have worked was to se a scribing bit in my dremel to free hand scribe a groove around the track. I figured the dremel being a lot lighter would allow me more control - I have one of those routing attachments that would have sat flat on the track. I then planned to use the big router to follow this groove.
cheers
David