If you call DL, a phone agent should be able to ticket it with a DL flight number.
"Should" is the key word here...I called 3 times yesterday to the Diamond desk and the 3 agents I got were clueless...and that's why I called back 3 times hoping to get someone that knew the difference between Delta One and AF La Premiere first class.
It's really crazy, but I can almost book a RT in La Premiere at a comparable price to several cities in Europe as I can in business class with most SkyTeam members. I'm great on MQMs for the year (as many are) but short on MQDs (hence the reason I want it to be on a Delta marketed DLxxxx flight).