Quick and easy transitions?

Hi. I have a pony that I love to bits, but is EXTREAMLY stubborn. To get him to go to a faster gait, you have to constanly ask him for half way across the arena on an aveage day. (sometimes he listens quite well and others not.) I am starting to get pretty annoyed at this, and wanted to know if there is anyway to get snappy transitions from him? (NOTE: he is not like this the entIre time, usually just the 1st 15 minutes of riding. However he is still relcuctant to change gaits.) We already know pain or uncomfort is not a component! So any advice or knowlage to share? Thanks~