I'd wait for a maint window then make the DB read/write, add the user and then reset to read-only.
USE [master]
GO
ALTER DATABASE [SomeDB] SET READ_WRITE WITH NO_WAIT
GO
CREATE USER [SomeUser] FOR LOGIN [SomeDomain\SomeUser]
GO
USE [SomeDB]
GO
GRANT SELECT ON SCHEMA::[dbo] TO [SomeUser]
GO
ALTER DATABASE [SomeDB] SET READ_ONLY WITH NO_WAIT
GO
_____________________________________________________________________
- Nate
@nate_hughes