I don't believe there's anything in the Runtime SDK that will do this for you, as the Runtime is part of and primarily integrates with the ArcGIS platform. If it's at all possible for you to leverage the platform to store your data, that's going to provide you with a clear and supported path for storing, viewing, and updating your polylines. Outside of that, it's technically possible to implement your own logic to store this data in a SQL server database using .NET components that exist outside the Runtime, but you'd presumably be on your own in getting that working and troubleshooting issues.
