Lewis, in addition to what Colin suggested, also try the first mob in this video: http://www.mobilitywod.com/daily/tuesday-february-3rd-2015/

I’ve had issues in the same area and this banded distraction has become a go to for me. 
Also try putting the gemini horizontally inside each scap and doing backstroke as you lie on the floor. You can also rotate the hand, come in from the top of the opposite leg etc. You may also benefit from putting a lacrosse ball under each trap, bridging your hips up and doing snow angels and backstroke. Even though these mobs will be above the trouble spot you describe, they might feed slack downstream and provide some relief.