Are you saying that if someone from Google tried to view your application then the request would fail? That would most likely be against the terms of use. I'll let you resolve that with Google directly.
If you know which routes you need to display then you should pre-geocode them and store then in your database, like you mention. The easiest way is to serialize the directions to a JSON string and store it as a string. This means that you would need a computer with access to Google's services. Otherwise have a look at http://www.reimers.dk/webservices/AtlasService.svc which also exposes a directions service, but it does track requests for statistical purposes.
The Reimers.Map.Accessories.MapUtils class has a JsonSerializer property which returns a serializer for just that purpose. Simply pass your directions to the Serialize method to get the string or pass the string to the Deserialize method to get the directions.