In the grand scheme of things, does it matter which is the Point of Turnaround in this itinerary ?
If it is a choice between a stopover in CDG on the way to BCN, or a stopover in BCN on the way to CDG, just book whatever AP will allow. The net result is the same.
And if they won't let you do either for some reason just book it as an open jaw and take the train or an LCC between Paris and Barcelona.