I'm trying to calculate mileage runs on the United website. I need 4345 more miles and i'm based out of NRT. If I fly to GUM on business I will hit that number for around $800... However, economy seats are much cheaper, around 200 and I would only need the equivalent of a one way business flight to GUM and an economy back. However it won't let me price that type of itinerary at any sort of reasonable price.. Also tried doing the same with a code share ANA domestic flight.

Did all the airlines figure out to not let you do such things like this?