I have this problem every now and then with my current girl friend. She would get so frustrated if I would blow my load before she was finished. So then she came up with the idea that if I cum before she did I would have to clean her out and with my tonge. This worked for quite awhile up until about 3 months ago until then I had never tasted cum and didnt have the desire to. Now I enjoy cleaning her out so it isnt helping but may work in your situation.