You could also encourage him to try deep belly breathing when he is getting close to the point of no return. There is a pretty good book called 'The multi-orgasmic male' that one can pick up on amazon.com pretty cheap. I think I got my copy for about 8.50 USD, and that included shipping. The breathing technique is one listed in that book.
Also, besides the belly breathing when he is getting close to the point of no return, stop all genital stimulation and let him regain his composure while focusing on his deep breathing. Works very well. And besides that little break can give him a chance to focus on other activities on other parts of your body to stimulate you further. Sex isnt just about bumping uglies.