That won't work.

In FB, when you retroclaim, it will "claim" not only the flight that you want, but all associated sectors on the same booking. Even if an earlier sector had been earmarked for another programme, the miles for that sector will not have been granted yet; and definitely for any AFKL operated "earlier" segments for which miles have not yet posted elsewhere, they will then also be "taken" and put into FB.

The only way the OP could hope to achieve this outcome is to have an agent remove the DL number and insert the FB number while on the ground at CDG. This may not be possible if the layover is tight; even if the agent does this, it could still work out in a way other than what the OP wants:

http://www.flyertalk.com/forum/air-f...g-account.html
http://www.flyertalk.com/forum/delta...f-account.html

It's possible to have more than one FFP number associated with a flight/booking; in such cases, it's anyone's guess as to which of the plural valid accounts would be selected for the miles.

Here's a personal example from the recent past showing, on a KL booking, an Alitalia Millemilglia number (twice!) and a Flying Blue number being associated with a single AFKL booking (viewed via the Garuda website):