I feel you have done a thorough enough examination, but meanwhile I liked to suggest other possibilities, some rather unlikely others more likely.
Digestive problems? since the pain starts around 12-2 PM it could have to do with indigestion (but not very likely due to the aggrevation).
Active triggerpoints in the area, You have to check thouroughly both dorsal and ventral, check with p.e. referred pain charts if the patern of your patient resembles any of the triggerpoints on the charts. If there is any resemblance check it out!
You do mention the all clear for the thoracic spine but what about the costo/vertabral joints?
I have had a patient with the Tietze's Syndrome, I guess, I chose at the time after having tried several devices like ultra sound because of the highly irritable state of the problem without any effect and send the patient back for injection therapy (which I did and do not like). I did not though checked out the suggested alternatives! (one learnes and thinks every day) A possible low irretable means would be taping of the costchondrial area although I would have no clue how to succeed.
Best of luck