You have to REPLACE the behavior with another, that means going WAY over the edge and hopefully the brain with then replace it. So, a couple of thoughts: turn the thumbs OUT (fingernails to the ceiling); That will close the elbows to the trunk/ribcage. The second is that you like have your hands too lowered and the arms in front of you, sit up/bend elbows/raise hands. Third is are you properly using the different reins effects (at least 3 of the five)?
It is NOT one time, it is a 1000s. Supposedly it takes 10,000 tennis swings to make a new one. That means if you think/act 100 x a day, it will take 3 years to replace the habit (based on riding 300 days a year). OR you can think/act on it 1000 times a day, and it will take 3 months. Your body, your choice.