I did this, unintentionally, with the cheap fares IAD-IST. Bought that first, then tried to get myself to IAD via another airline's award ticket. Ended up finding cheap r/t to IAD on DL that I partially paid for with Amex MR points. So now I have exactly that, showing as two separate trips on DL.com. I'm afraid to ask them to combine them into a single trip, as the lovely DeltaMatic may reprice it and decide I owe them $50384590 in fare difference (plus $150 change fee).
