In rereading this, Hobbes, I realize that you make a very important and terrific observation: unlike any other service I know, the Osmand app allows the user to create routes and save them as gpx files, all done while the phone or tablet is off-line. This feature should not be taken lightly. It indeed makes possible the feature you have discussed. Even if a cyclist is away from all wifi and data connections on an African safari, he can still use the Osmand app to create and save any number of gpx tracks. This really works!! Amazing!! Using a travel router such as the HooToo Nano properly connected to an android device, the saved files can then be transferred to any turn by turn capable device with disk drive using NTFS, FAT 16/32 file structure. I know that this works with a Garmin Edge 500, but obviously includes many devices. If you can connect a PC via usb to any bike computer and transfer gpx/tcx files to its routes or courses file folder, then this should all work as described earlier in this thread. Tip: to find gpx files saved by Osmand on android devices, go to Android/data/net.osmand.dev/files/tracks.

Note: although iOS devices will connect to a router, only limited file sharing is permitted. As I recall you can only share photos, videos, and music after connecting an iPad to the Hootoo Nano.