That ought to do it. It's called a "vibrating cock ring" and they are available everwhere (even at Target). You can get vibratory stimulation while having intercourse with no manual effort. The added penile pressure will help him to last even longer than he does, and both of you are happier for it.

About the best position for the use of this type of toy is the cowgirl (girl on top). That way you can control the position of contact, pressure, rhythm, and penetration.

I hope this helps you.
~Steve