I think you'll have to manually create the connection string as the IDE won't automatically generate ones connecting to SQL Server Standard Edition. But you can easily record two in the app - one for testing that points to the EXPRESS instance, and one for the live that points to the real one. As long as you're connecting to the same objects and interacting with them in the same way, it should be fine.
You can manually amend your connection string AFTER the IDE has generated its own to something like :
Data Source=ServerName;Initial Catalog=AppDatabase;Integrated Security=True;Persist Security Info=True;Connect Timeout=30
replacing ServerName and AppDatabase as required, and with possible authentication changes. You'll have to watch for the IDE recreating the original connection string, though, as I can't see a way to modify the connection string used in the Database Explorer and if you use the IDE to drag datasources into your app it'll keep using the original connection string.
SQL Server Developer Editions are pretty cheap, though - easily less than £50.