I'm managed to add the right function to Navit that you can select it for as default routing application.

All it needs is to add "mimeTypes": [{"scheme": "mapto"}, {"scheme": "maploc"},{"scheme": "telenav"}] to appinfo.json
Then you can access the requested destination as a mojo launch parameter.

You can find my testing code in that commit:
git.webos-internals.org Git - applications/navit.git/commitdiff

I expect this will work for the other default apps too if you know the right sheme parameter.