DL has some relatively cheap BOS flights in first over the next couple of months, mostly by virtue of a cheap BOS-ATL biz fare that pops up occasionally, from what I can tell. So just looking at 0-day turns, best itinerary I can find is BOS-ATL-TPA-CVG-BOS for $416, which generates 4,457 MQM at 9.3 CPM, booking into G and Z.
A more expensive routing that maximizes miles: BOS-MSP-TPA-MSP-BOS, leaving 11/18, returning 11/21. $567.20, generates 7,290 MQM at 7.8 CPM, booking into G on the outbound and P on the return.