You could buy the BOS - ORD on another airline (just giving up the points / status for that one flight seems worth it to preserve the rest) to avoid any issue with the DL system having problems with overlapping bookings and then just cancel the final leg after the fact or just miss the flight and it'll be canceled for you.
With the B6 waiver in place you could book with them and have a with free cancellation if you are able to make something with DL work (though they only credit back as a travel credit, not full refund).