Originally Posted by
Oxymore
Have you tried asking DL to open up space on one of their own flights? They should indeed be willing to do that. Otherwise, the AF Twitter team can sometimes be helpful.
Other option is call AF and see if they would be willing to add their own flight segment in the reservation, then call DL back for re-ticketing.
Odd that DL/AF are giving the OP a hard time with this... at the very least DL could have opened up space on their own metal as you suggested.