I'm beginning to think that this might not be doable. I called again this morning to change a different itinerary, and then had the agent look into it (4th attempt, 5th if you count Twitter). She verified that my itinerary qualified for all the rules, but the system still wasn't showing her the ability to apply it. She explained it was a yes/no situation and that, while I should be able to apply my SWU, she just simply wasn't able to do it and advised I keep trying. The only thing she could do was make a training note about it.