I think Greg is right - I have a GPS V and I don't think this has this feature. Only thing you could do is stop the route - save the track log and then tracback to beginning - this should take you back the way you came to the point where the track log started recording that particular log.
Let us know if you find another way.
Cheers
Gecko
Well I cant find a way of doing it. Seems stupid to me having gone to the trouble of creating complex routes, also combined with the fact that you cant load many waypoints. Oh well.