Well, you could just sit back and refrain from dating until he finds somebody. If you haven't met somebody you really click with thats not the worst idea. You wont DIE if you dont take advantage of all the great opportunities the world presents women (seemingly) more than men in poly.
Do you guys use OKcupid or another dating site? Help him edit his profile to be more attractive a representation of what he has to offer.
One thing I've learned is if you can tell somebody is stressed, just because they don't say they are distressed doesn't mean you shouldn't listen to what they are non verbally saying and doing. Some people just haven't learned how to speak up, and I'd sure rather be cautious than be sorry for it later.
Happiness will never come to those who fail to appreciate what they already have.