Load route into Mapsource.
Decide haow many sections you want to break it into.
Right click on the route and select "duplicate" Repeat this until you have enough copies for each section, each day for example.
Rename a copy, day 1, open it and delete all the points after day 1 final destination.
Rename next copy day 2 and delete all the "non day 2 points".
Repeat for rest of the required sections.
Save everything as a Mapsource file
Delete the original full route and send all the sections back to the Zumo.
There may be a quicker way but I haven't found it and this takes longer to type than to do.