Sam,
Here you go.. (click to enlarge drawing)

With this arrangement, I would try and center the point (as I've tried to show) where the linkage goes through the crossmember. A brass tube inside that hole will help eliminate wear on the wood. Piano wire about the size they supply with the tortise shold be used to maintain some springyness. Perhaps a little thicker. You may have to experiement with different locations (up or down) for the cross point to get one that works right. This is only an idea of mine, I've never actually tried it.
Good luck..
Edit: Now that I've thought about it for a minute, you probably want the fulcrum higher to minimize the throw on the other end of the link. Just like if you were installing the tortise normally. I forgot you are doing N scale so you really don't need that much movement on the point end.