Maybe you can do it manually. For example if you want to loop and reduce for the field Country. Select the first country that you want to reduce in your application and then go to File -> Reduce Data -> Keep Possible values. Now with this option the data model has been reduced only with the selected selections, in your case the Country information. To not override the file, save the file with a new name, something like FileName_CountryName.qvw.
The problem of this method is that you will need to go Country by Country.
The best way is to have a publisher to do loop and reduce.