With Mapsource you can transfer OSM maps without the routing data to your device.
Unable the include route calculation data when sending it to your device:
Then you have to make sure the OSM map has a higher draw priority than the OFM. To do this you need to install gmaptool.
See the picture on http://www.gmaptool.eu/en/content/map-visible-basecamp, fill 21 in the field “set draw priority” (the OFM and the OSM Generic New Style both have 20 as draw priority).
On your device, make both maps active. If everything works well, the underlying OFM will take care of the routing but will be invisible.
The routing of the OSM map is removed so it will not mess up with the OFM.
