This can be done on the DL web site or any site hosted by ITN (UA, AMEX corp travel, AAA, etc). You simply pick the "multi city" flight request and enter the segments individually with the approximate connecting times. This does take some knowledge (which you likely have) of what connections and general times are available. The computer will automatically price the selected itinerary for the lowest fare.

In addition, the ITN sites give experienced users the opportunity to view class of service availability by number of seats (i.e. F,Y,B,Q,H,K,and the dreaded L),which can be very helpful for those wishing for upgrades or stand-by opportunities.