Creating a custom migrations cfg for a particular context:
enable-migrations -ContextTypeName HereGoes.Custom.Context.TypeName -ConnectionStringName IfNeeded -MigrationsDirectory LetsCustomiseMigrationsStorage
Adding a custom migration for a specific configuration:
add-migration -ConfigurationTypeName HereGoes.Custom.MigrationsConfiguration.TypeName
Updating a database using custom migration configuration:
update-database -ConfigurationTypeName HereGoes.Custom.MigrationsConfiguration.TypeName -ConnectionStringName IfNeeded