What if you cancelled the run altogether and put the money towards upgrading your work trip? If that gets you the miles you need, you could save flying time and enjoy a more comfortable transcon flight.
I'm MVPG, so no change fees. I loved this solution, which didn't even cross my mind because my brain has been programmed to avoid all additional perceived aggravation for our admin staff. Unfortunately, the difference between the work fare and paid F round-trip is far more expensive than the $900 I'd save cancelling the mileage run (at least for any flight I would actually want and that wouldn't create more admin hassle by extending my time in travel status).