Since this is in the DL forum, I will say that based on anecdotal evidence from Flyertalk, DL is very vigilant about enforcing the ban on back-to-back ticketing. DL is definitely the last airline I'd try to get away with this on.

I just started working for a new company, and they us back-to-back ticketing sometimes, but they use US Airways and they haven't been caught ... yet. If it's me, I'm not risking my status/miles, and if I ever need to use back-to-back ticketing, I will just do it on two airlines ... there is no way they could catch you then.

As for having the mileage put in after the fact by sending in the boarding passes ... still sounds pretty risky with DL.